MMD    1M7 


MEMCA 


PHYSIOLOGY  FOR  NURSES 


—Skull 


\ — Cervical  vertebra; 


:- — Scapula 


— Dorsal  vertebrae 


— Lumbar  vertebrae 


PROFILE  OF  SKELETON. 


A  TEXTBOOK  OF 
PHYSIOLOGY  FOR  NURSES 


BY 


WILLIAM  GAY  CHRISTIAN,  M.D. 

Professor   of   Anatomy,   Medical   College   of   Virginia 
AND 


CHARLES  C.  HASKELL,  M.A.,  M.D. 

Professor  of  Physiology  and   Pharmacology,  Medical   College   of   Virginia 


ILLUSTRATED 


ST.  LOUIS 

C.  V.  MOSBY  COMPANY 

1918 


COPYRIGHT,  1918,  tty  C.  V.  MOSBY  COMPANY 


Press  of 

C.  J'.  Mosby  Company 
1918 


PREFACE 

It  is  presumed  that  the  pupil  nurse,  for  whom  this 
book  has  been  compiled,  is  familiar  with  the  writer's 
Anatomy  for  Nurses,  and  has  a  similar  knowledge  of 
physics  and  chemistry.  Technical  terms  have  been  em- 
ployed, without  full  explanation,  upon  this  assump- 
tion. A  brief  appendix  containing  an  outline  of  some 
physical  and  chemical  phenomena  has  been  added  for 
those  who  have  not  received  a  proper  introduction  to 
these  subjects. 

In  the  preparation  of  the  work  we  have  chiefly  re- 
lied on  the  work  of  Luciana,  Howell,  Pearce-Macleod, 
Jones  and  Bunce,  Mallet's  Syllabus  of  Chemistry, 
Ganot's  Physics,  and  Bliss  and  Olive's  Physics  and 
Chemistry  for  Nurses.  The  work  is  an  elementary  one 
and  has  no  claim  to  originality  except  in  arrangement 
and  treatment. 

W.    G.    CHRISTIAN. 
C.  C.  HASKELL. 

Richmond,  Va. 


560;" 


CONTENTS 


CHAPTER  I 
- 
CIRCULATION 17 

CHAPTER  II 
RESPIRATION i     34 

CHAPTER  III 
FOOD    AND   DIGESTION , 43 

CHAPTER  IV 
THE  FUNCTIONS  OF  THE  LIVER 76 

CHAPTER  V 
THE  SPLEEN 80 

CHAPTER  VI 
FUNCTIONS  OF  THE  KIDNEY 82 

CHAPTER  VII 
THE  FUNCTIONS  OF  THE  SKIN 90 

CHAPTER  VIII 
THE  DUCTLESS  GLANDS 94 

CHAPTER  IX 

THE  NERVOUS  (SYSTEM 1M) 

U 


12  CONTENTS 

CHAPTER  X 
THE   SPECIAL   SENSES 122 

CHAPTER  XI 
SLEEP 138 

CHAPTER  XII 

• 

REPRODUCTION 142 

CHAPTER  XIII 
GROWTH  AND  OLD  AGE 145 

APPENDIX 
APPENDIX 147 


ILLUSTRATIONS 


FIG.  PAGE 

Profile    of    Skeleton Frontispiece 

1.  Simple  tissues 18 

2.  White    blood    corpuscles    from    man 20 

3.  Diagram   of  entire   circulation 22 

4.  Diagram  of  valves  of  the  heart 25 

5.  Cross  section  of  small  artery  and  veins:    A,  artery;  V,  vein  27 

6.  The  aorta  and  its  branches 28 

7.  Apparatus   for   measuring   the   arterial   blood   pressure   in 

man 31 

8.  The  position  of  the  lungs  in  the  thorax     .......  35 

9.  Diagram  of   structure   of  lungs  showing  larynx,  bronchi, 

bronchioles,  and  alveoli 36 

10.  Front    view    of    organs.      Semidiagrammatic 49 

11.  Diagram  of  the  alimentary  tube  and  its  appendages     .     .  52 

12.  The  stomach  and  duodenum  opened 56 

13.  Schema  of  simple  reflex  arc 58 

14.  Cross  section  of  pancreatic  tubule 60 

15.  Injected  lacteal  vessels  in  two  villi  of  human  intestine     .  63 

16.  The  microscopic  structure  of  the  liver 77 

17.  Portion  of  transverse  section  of  human  liver 78 

18.  Vertical  section  of  human  spleen 80 

19.  Longitudinal  section  through  the  kidney 85 

20.  Diagrammatic  representation  of  the  course  of  the  urinifer- 

ous  tubules  and  the  kidney  vessels 86 

21.  The   thyroid   gland 95 

22.  Schema  of  simple  reflex  arc 100 

23.  B-rain,  lateral  view 101 

-4.  Cortical  centers  in   man 103 

25.  Brain,  mesial  view 104 

26.  Diagram  of  section  of  spinal  cord,  showing  tracts     .     .     .  Ill 

13 


14  ILLUSTRATIONS 

FIG.  FAfiK 

27.  The  simplest  reflex  arc  in  the  spinal  cord 112 

28.  Orbital   muscles 126 

29.  Section  through  the  anterior  portion  of  the  eye     ....  127 

30.  Formation  of  image  on  retina 129 

31.  Errors  in  refraction 132 

32.  Tympanum  of  right  side  with  the  auditory  ossicles  in  place  134 

33.  Semidiagrammatic  section  through  the  right  ear     ....  136 

34.  Diagrammatic  view  of  the  organ  of  Corti     ......  136 


PHYSIOLOGY  FOR  NURSES 


PHYSIOLOGY  FOR  NURSES 


CHAPTER  I 

CIRCULATION 

Just  as  anatomy  is  a  study  of  form,  physiology  is  a 
study  of  function.  Anatomy  studies  the  appearances  of 
the  bones,  ligaments,  muscles,  vessels,  nerves  and  vis- 
cera, by  dissecting  the  dead  body.  Physiology  explains 
that  bones  are  supports  and  levers;  ligaments,  binding 
tissue ;  muscles,  moving  agents ;  vessels,  channels  for  cir- 
culating fluids;  nerves,  conducting  agents;  viscera, 
agents  of  secretion  or  excretion  necessary  for  life  and 
growth.  Physiology  can  not  be  learned  from  the  dead 
body,  though  some  of  it  can  be  guessed  at,  but  must  be 
discovered  by  observation  of  the  living  animal  or  plant. 
Examination  and  analysis  of  the  cells  of  which  bodies 
are  composed  may  reveal  their  physical  and  chemical 
character,  but  the  more  thorough  the  analysis,  the  more 
complete  the  destruction  of  the  cells  and  the  more  impos- 
sible it  is  to  investigate  their  vital  activities.  Hence  many 
vital  phenomena  are  still  unexplained,  though  the  num- 
ber is  daily  decreasing. 

The  most  widely  distributed  of  all  the  tissues  of  the 
body  is  the  blood.  It  is  the  universal  solvent  for  all  ma- 
terial used  in  building  other  tissues,  in  keeping  them  iii 
a  state  of  health  by  carrying  food  to  them  and  by  remov- 
ing worn  out  or  injurious  material  from  them.  The  func- 
tions of  the  blood  and  the  forces  of  the  circulation  make, 

17 


18 


PHYSIOLOGY   FOR   NURSE8 


I 


CIRCULATION  19 

therefore,  a  convenient  point  of  departure  in  beginning 
the  study  of  physiology. 

The  blood  consists  of  a  liquid,  plasma,  and  solid  bodies, 
red  corpuscles,  or  erytlirocytes,  blood  platelets;  and 
white  corpuscles,  which  are  of  two  kinds,  leucocytes  and 
lymphocytes. 

The  plasma  is  all  of  the  liquid  part  of  the  blood  as  it 
exists  in  the  living  animal  and  is  to  be  distinguished  from 
"  serum, "  which  is  the  liquid  part  after  coagulation  Jias 
occurred.  Plasma  consists  chiefly  of  water,  but  contains 
other  substances  of  the  greatest  importance.  The  inor- 
ganic salts,  such  as  sodium  chloride,  calcium  chloride, 
and  potassium  chloride,  as  well  as  compounds  of  these 
bases  with  other  acid  radicals,  are  of  importance  in  re- 
gard to  the  phenomena  of  osmosis,  as  influencing  the  ir- 
ritability of  muscle  and  nerve,  and  are  supposed  to  play 
an  important  role  in  the  maintenance  of  the  heart  beat. 
Calcium  salts  cause  an  increased  vigor  of  contraction 
and  if  present  alone,  cause  the  heart  to  stop  tightly  con- 
tracted; while  the  salts  of  potassium  tend  to  cause  re- 
laxation. It  is  suggested  that  the  presence  of  these 
salts  in  proper  concentrations  causes  the  alternate  con- 
traction and  relaxation  of  the  heart  during  life. 

Among  the  organic  constituents  are  proteins,  which 
are  known  as  fibrinogen,  serum  albumin,  and  serum  glob- 
ulin or  paraglobulin.  In  addition,  there  are  what  may  be 
designated  as  temporary  constituents  of  the  plasma,  sub- 
stances on  their  way  from  the  digestive  canal  to  the  tissues, 
such  as  fat,  sugar,  the  results  of  protein  digestion;  as  well 
as  waste  products  on  their  way  to  the  organs  of  excre- 
tion; bodies  known  as  hormones,  which  are  produced 
at  one  part  of  the  body  and  sent  elsewhere  to  influence 
other  structures;  substances  which  are  manufactured  to 
enable  the  animal  to  overcome  bacterial  invasion;  and 


20  PHYSIOLOGY   FOR   NURSES 

certain  substances  which  resemble  ferments  in  their  ac- 
tion. Among  the  latter  may  be  mentioned  protlirom- 
bin,  which,  as  we  shall  see,  is  active,  in  causing  blood- 
clotting  or  coagulation. 

Of  the  formed  elements  of  the  blood,  the  red  corpus- 
cles or  erythrocytes  are  the  most  numerous.  There  are 
about  five  million  of  these  to  the  cubic  millimeter  of  the 
blood  of  a  healthy  man  ;  women  are  supposed  to  have 
about  five  hundred  thousand  less.  They  contain  a  sub- 
stance known  as  hemoglobin,  which,  by  virtue  of  its 
iron  content,  is  capable  of  forming  unions  with  gases, 
especially  with  oxygen,  and  to  a  less  extent  with  car- 
bon dioxide.  These  unions,  as  we  shall  find,  are  essen- 


Small  Large  Polymorphic  Polynuclear.  Eosinophile. 

mononudear.  monomiclear. 

Fig.   2.  —  White  blood-corpuscles  from  man.      (Hill's  Histology.) 

tial  for  the  processes  of  respiration.  The  number  of 
these  corpuscles  is  reduced  under  certain  pathologic 
condition,  as  in  the  various  anemias;  and  may  be  in- 
creased when  there  is  a  great  loss  of  fluid  from  the  body, 
as  in  cholera  or  where  there  is  a  diminution  in  the 
amount  of  oxygen  in  the  surrounding  air,  as  in  ascents 
to  great  heights. 

The  white  cells  serve  an  entirely  different  function  in 
the  body.  There  are  from  five  to  ten  thousand  to  the 
cubic  millimeter  of  blood  on  the  average,  but  this  num- 
ber is  subject  to  wide  variations  under  altered  condi- 
tions. The  white  cells  are  of  assistance  in  the  digestion 
of  protein  and  in  the  transportation  of  fat  in  the  blood, 


CIRCULATION  21 

which  probably  explains  the  increase  in  their  numbers 
following  a  meal.  Cold  baths  and  pregnancy  are  other 
''physiologic"  causes  of  increased  numbers  of  leuco- 
cytes. A  very  important  duty  of  the  white  cells  is  to 
combat  bacterial  invasion,  and  it  is  found  that  many  in- 
fectious diseases  are  accompanied  by  an  increase  in  the 
number  of  the  leucocytes.,  this  leucocytosis  often  being  of 
value  in  the  diagnosis.  In  pneumonia,  for  instance,  the 
number  not  infrequently  is  increased  to  forty  or  fifty 
thousand  to  the  cubic  millimeter.  In  the  leucemias, 
there  is  often  a  still  larger  increase ;  while  in  some  other 
diseases,  such  as  typhoid  fever,  there  is  a  reduction 
in  the  number,  this  being  known  as  a  leucopenia. 

There  are  about  three  hundred  thousand  platelets  to 
the  cubic  millimeter.  These  are  small  disc-shaped  bodies 
when  examined  with  proper  care,  but  usually  disinte- 
grate and  appear  simply  as  detritus  in  the  ordinary 
stained  specimens  of  blood.  Their  functions  are  imper- 
fectly understood;  they  appear  to  be  of  importance  in 
the  coagulation  of  the  blood,  and  it  is  claimed  that  their 
number  is  reduced  in  the  hemorrhagic  diseases. 

Lymph. — It  must  be  understood  that  the  tissue  cells 
are  not  bathed  direct  in  blood.  The  blood,  carried  in  its 
system  of  vessels,  has  been  likened  to  a  wholesaler,  and 
the  pnrt  of  the  retailer,  coming  in  intimate  contact  with 
the  consuming  tissue  cells,  is  taken  by  the  lymph.  The 
lymph  is  derived  from  the  blood  by  the  processes  of  fil- 
tration and  osmosis,  and  is  poured  out  into  the  spaces 
surrounding  the  cells.  Containing  the  nutritive  sub- 
stances derived  from  the  blood,  it  turns  these  over  to  the 
cells  and  receives  waste  products  from  the  latter.  It  is 
forced  into  special  vessels,  knoAvn  as  lymphatic  chan- 
nels, and  finally  is  carried  back  into  the  blood  stream 
through  the  right  and  left  lymphatic  ducts.  Along  the 


22  PHYSIOLOGY   FOR   NURSES 

course  of  the  lymphatic  channels  are  found  the  lym- 
phatic glands,  which  act  as  niters,  attempting  to  prevent 
the  entrance  of  bacteria  or  toxins  into  the  circulation. 
The  "waxen  kernels"  are  lymphatic  glands  that  have 
become  inflamed  and  swollen  as  the  result  of  the  action 
of  some  toxic  agent. 

Coagulation. — The  clotting  or  coagulation  of  the 
blood  is  nature 's  way  of  stopping  hemorrhage  and  where 
there  is  derangement  of  the  process,  serious  or  even 
fatal  hemorrhage  may  occur  from  an  apparently  trivial 
wound.  A  substance  known  as  prothrombin  and  salts  of 
calcium  is  found  in  the  blood.  If  calcium  acts  on  pro- 
thrombin, it  converts  the  latter  into  thrombin  and  throm- 
bin  causes  fibrinog'en,  a  soluble  protein  of  the  blood 
plasma,  to  assume  an  insoluble  form,  known,  as  fibrin, 
this  latter  constituting  the  clot,  enclosing  the  red  corpus- 
cles in  its  meshes.  The  white  cells  possess  the  power  of 
movement,  so  they  are  not  included  in  the  clot  to  any 
considerable  extent.  That  blood  does  not  normally  clot 
in  the  vessels,  is  explained  by  the  presence  of  a  substance 
known  as  antithrombin,  which  prevents  the  action  of  the 
calcium  salts  on  the  prothrombin.  When  tissues  are 
wounded,  another  substance,  known  as  kephalin  or 
"thromboplastic''  substance,  neutralizes  the  antithrom- 
bin and  allows  the  conversion  of  prothrombin  into  active 
thrombin.  If  blood  is  obtained  by  puncturing  a  vein  and 
drawing  the  blood  into  a  perfectly  clean  syringe,  contact 
with  wounded  tissue  is  prevented  and  coagulation  is  de- 
layed, because  the  thromboplastic  substance  is  not  de- 
rived from  passing  over  wounded  tissue.  Clotting  will  oc- 
cur, however,  because  the  platelets  will  gradually  dis- 
integrate and  furnish  the  requisite  thromboplastic  ma- 
terial. The  hemorrhagic  diseases  which  have  been  men- 
tioned, are  accompanied  by  a  marked  increase  in  the 


Fig.    3. — Diagram   of    entire   circulation. 


CIRCULATION  23 

coagulation  time,  so  that  individuals  have  bled  to  death 
after  the  extraction  of  a  tooth  or  the  production  of  sim- 
ilar small  wounds. 

The  circulatory  apparatus  consists  of  a  central  pump- 
ing station,  the  heart;  a  set  of  vessels  leading  from  the 
heart  to  all  portions  of  the  body,  the  arteries;  an  im- 
mense number  of  small  thin-walled  vessels,  the  capilla- 
ries, in  which  the  arteries  terminate;  and  a  set  of  ves- 
sels, the  veins,  which  return  the  blood  to  the  heart.  The 
schematic  drawing  shows  that  arteries  constantly  dimin- 
ish in  size  as  they  get  further  from  the  heart,  that  the 
capillaries  are  the  terminations  of  arteries  and  begin- 
ning of  veins,  and  that  the  veins,  by  one  vein  joining  an- 
other, increase  in  size  as  they  approach  the  heart.  The 
total  area  of  capillaries  is  greater  than  that  of  the  veins 
and  much  greater  than  that  of  the  arteries.  If  the  blood 
in  the  arteries  differs  from  that  in  the  veins,  it  is  obvious 
that  there  must  be  a  sort  of  midpoint  in  the  capillary 
system  where  arterial  changes  to  venous  blood;  and  if 
this  is  true,  it  is  apparent  that  the  arteries  carry  some- 
thing to  the  tissues  which  they  need  and  that  the  veins 
take  something  away  which  is  either  useless  or  inju- 
rious. The  object  of  the  circulation  of  the  blood  is,  there- 
fore, briefly,  to  feed  or  irrigate  the  tissues  through  the 
arteries  and  to  drain  them  through  the  veins.  But  the 
veins  can  not  pour  out  the  blood  so  charged,  because  it 
would  waste  the  blood  which  can  be  purified;  so  the 
lungs  liave  been  provided  to  burn  up  the  waste  material 
and  change  venous  back  to  arterial  blood  which  is  fur- 
ther cleansed  by  the  liver  and  kidneys.  The  course  of 
the  circulation  is  then  from  the  heart  through  the  arter- 
ies and  capillaries  to  the  tissues  where  arterial  is 
changed  to  venous  blood;  through  venous  capillaries 
and  veins  to  the  heart  and  thence  to  the  lungs  where 


24  PHYSIOLOGY   FOR   NURSES 

venous  is  changed  to  arterial  blood  and  thence  back  to 
the  heart  to  go  over  the  same  route  as  long  as  life  lasts. 
The  heart  is,  therefore,  the  main  force  of  the  circula- 
tion. Anatomy  has  taught  us  that  it  is  a  four-chambered 
hollow  muscle.  The  two  thin-walled  chambers  at  the 
base  are  called  auricles,  the  two  thick-walled  chambers 
forming  the  apex,  the  ventricles.  Both  the  left  auricle 
and  ventricle  are  thicker  than  the  right,  but  the  left 
ventricle  is  much  thicker  than  any  other  part  of  the  or- 
gan. The  right  half  is  concerned  with  venous  blood  and 
the  pulmonary  circulation.  The  blood  from  the  upper 
extremities,  head  and  neck  is  collected  and  poured  into 
the  right  auricle  through  the  superior  vena  cava;  that 
from  the  lower  part  of  the  body  enters  the  same  cavity 
through  the  inferior  vena  cava.  From  the  right  auricle 
the  course  is  into  the  right  ventricle  through  the  auric- 
iiloventricular  opening,  thence  through  the  pulmonary 
artery  into  the  lungs  whence  it  is  collected  by  the  four 
pulmonary  veins  and  carried  into  the  left  auricle  from 
which  it  flows  through  the  left  auriculoventricular 
opening  into  the  left  ventricle  from  which  it  is  pumped 
through  the  aorta  to  all  parts  of  the  body. 

The  auriculoventricular  openings  are  guarded  by 
valves  composed  of  triangular  flaps,  the  right — tricuspid 
—having  three,  and  the  left — bicuspid,  or  mitral — hav- 
ing two.  The  two  auricles  fill  at  the  same  time.  As  the 
blood  flows  in  through  cavse  or  pulmonary  veins,  it  passes 
through  the  auriculoventricular  openings  into  the  cor- 
responding ventricle  until  that  cavity  is  nearly  full.  As 
the  blood  rises  in  the  ventricle  it  floats  the  valve  flaps 
away  from  the  walls  of  the  ventricles  and  toward  the 
opening.  This  action  continues  until  there  is  but  a  slit- 
like  aperture  between  the  flaps.  Just  at  this  moment 
the  auricle  contracts,  forces  into  the  ventricle  all  the 


CIRCULATION 


25 


blood  it  will  hold  and  presses  the  valves  tightly  across 
the  opening-  into  which  it  would  project  if  the  papillary 
muscles  did  not  contract  and  hold  the  edges  of  the  valve 
at  just  the  right  angle.  This  action  of  the  auricles  is 
called  auricular  systole  (from  a  Greek  word  meaning 
to  contract).  With  a  barely  perceptible  pause  ventricular 
systole  begins,  the  blood  is  forced  into  the  aorta  and  pul- 
monary artery,  whose  openings  are  guarded  by  three 
cuplike  folds  called  semilunar  valves.  As  the  blood 
rushes  between  these  cups  some  of  it  gets  into  three  lit- 


Fig.  4. — Diagram  of  valves  of  the  heart.  The  valves  are  supposed  to  be 
viewed  from  above,  the  auricles  having  been  partially  removed.  A,  aorta 
with  semilunar  valve;  B,  pulmonary  artery  and  valve;  C,  tricuspid,  and  D, 
mitral  valve;  E,  right,  and  F,  left  coronary  artery;  G,  wall  of  right,  and  H, 
of  left  auricle;  /,  wall  of  right,  and  /,  of  left  ventricle.  (Stewart's  Physi- 
ology.) 

tic  pockets,  sinuses  of  Valsalva,  between  the  valve  folds 
and  the  arterial  Avails,  so  that  when  the  force  from  be- 
hind ceases  the  weight  of  the  blood  and  the  elastic  re- 
coil of  the  vessels  force  each  flap  towards  the  opening, 
and,  the  three  flaps  coming  together,  the  return  of  blood 
to  the  heart  is  prevented.  This  completes  the  contrac- 
tile or  systolic  period  of  the  heart  cycle  and  the  period  of 
rest,  diastole,  begins.  A  cardiac  cycle,  therefore,  con- 


26  PHYSIOLOGY   FOR   NURSES 

sists  of  two  distinct  parts;  i.e.,  auricular  systole,  ven- 
tricular systole,  and  diastole,  or  rest.  The  closure  of 
the  auriculoventricular  valves  takes  place  at  the  same 
instant;  that  of  the  semilunar  valves  a  little  later.  The 
sound  of  the  first,  dull  and  low  pitched  and  confused 
with  the  sound  made  by  contracting  muscle,  is  called 
the  first  sound  of  the  heart;  the  sharp,  high,  short  click 
of  the  semilunar  valves,  make  the  second  sound.  Cardiac 
systole  lasts  about  the  tenth  of  a  second,  diastole  about 
five  tenths;  so  that  the  heart  is  at  rest  about  sixty  per 
cent  of  the  time. 

Exact  closure  of  all  the  valves  is  necessary  to  prevent 
leakage.  It  follows,  therefore,  that  if  any  valve  is  too 
short  or  too  long,  has  a  rough  place  on  it  either  through 
the  presence  of  a  foreign  body  or  a  wound,  it  will  not 
meet  its  fellows  exactly  and  there  will  be  a  falling  back 
of  blood  into  the  chamber  which  that  valve  guards.  Or 
if  the  opening  is  too  small  from  any  cause,  there  will  be 
greater  difficulty  in  driving  the  blood  through,  or  it 
would  take  a  longer  time.  Either  defect  would  cause 
a  change  in  the  heart  sounds. 

Various  infectious  processes  are  apt  to  cause  such 
damage  to  the  valves  through  the  production  of  "endo- 
carditis," an  acute  inflammatory  process  involving  the 
inner  lining  of  the  heart.  When  the  inflammation  sub- 
sides, scar  tissue  appears  and,  as  is  always  the  case  with 
such  tissue,  contraction  causes  a  distortion  of  the  leaf- 
lets with  a  resultant  leakage.  Rheumatic  fever,  tonsil- 
litis, chorea,  and  pneumonia  are  the  commonest  predis- 
posing causes  for  endocarditis. 

The  heart  is  the  chief,  but  not  the  only,  force  of  the 
circulation.  The  arteries  are  lined  by  a  thin  coat — the 
Mima — continuous  with  the  lining  membrane  of  the 
heart ;  but  around  this  their  wralls  are  composed  of  fi- 


CIRCULATION 


27 


brous,  muscular  and  elastic  tissue.  The  latter  is  partic- 
ularly important.  If  fluid  is  put  into  an  iron  pipe  until 
it  is  full,  110  force  will  get  any  more  of  the  liquid  in ;  but 
if  the  same  experiment  is  tried  with  a  rubber  tube,  not 
only  can  an  additional  amount  be  forced  into  the 
stretched  tube,  but,  as  soon  as  the  power  is  withdrawn, 
the  additional  fluid  will  be  squeezed  out,  even  against 
gravity,  by  the  elastic  contraction  of  the  tube.  When 
the  heart  forces  blood  into  the  aorta,  that  tube  expands. 
As  soon  as  the  heart  ceases  to  contract,  the  elastic  coat 

.•f'^'^&ij&S&S^^''  v"^^%£^i?  -" 

:-M    A     ftoi       v      \ 


Fig.   5. — Cross    section    of   small    artery    and    vein:      A,    artery;    V,    vein. 
(Hill's  Histology.) 

of  the  artery  contracts.  If  the  semilunar  valves  hold,  no 
blood  can  return  to  the  heart  and  the  contraction  of  the 
elastic  artery  must  drive  the  blood  onward  into  the 
smaller  arteries.  The  elastic  recoil  of  the  arteries  them- 
selves, is,  therefore,  the  second  great  force  of  the  circula- 
tion and  one  which  acts  continuously.  The  heart  acts 
only  during  systole,  the  recoil  of  the  arteries  continues 
during  diastole.  As  the  arteries  diminish  in  size  they 
offer  greater  resistance,  partly  by  friction,  to  the  pas- 
sage of  the  blood ;  and  as  their  distance  from  the  heart 
increases  and  their  strength  diminishes,  the  heart's  im- 


28  PHYSIOLOGY   FOR   NURSES 

pact  and  the  elastic  recoil  both  lose  power  until,  in  mi- 
nute arteries  the  blood  flow  approaches  the  character  of 
a  steady  stream  instead  of  the  jet-like  type  of  the  larger 
arteries.  In  the  arteries  the  blood  leaps  in  jets ;  in  the 
capillaries  it  oozes;  in  the  veins  it  flows.  It  is  like  a 
swift  torrent  which  spreads  into  a  marsh  where  move- 
ment is  barely  perceptible  until  its  outlet  is  found  in  a 
deep,  dirty,  sluggish  stream. 

The  venous  current  is  collected  by  the  veins  from  the 
capillaries.  The  blood,  through  capillaries  and  veins, 
still  receives  an  impulse  from  the  heart,  but  not  in  suf- 
ficient strength  to  complete  the  return  circulation.  Cer- 
tain accessory  forces  are,  therefore,  called  into  play. 
The  first  of  these  is  the  suction  of  the  thorax  caused  by 
inspiration,  and  described  under  that  head.  A  more 
widespread  factor  is  that  of  the  valves  in  the  veins,  par- 
ticularly those  so  located  that  gravity  habitually  retards 
the  flow.  These  valves  are  half  cup  shaped,  concavity 
upward,  very  much  like  the  semilunar  valves,  so  ar- 
ranged that  the  blood  flows  easily  over  their  free  sur- 
face, but  is  caught  in  the  hollow  cup  when  it  attempts 
to  fall  back.  From  this  position  it  is  forced  on  to  the 
next  valve  partly  by  the  push  of  the  heart  from  behind, 
partly  by  suction  of  the  thorax  in  front  and  largely  by 
the  massage-like  action  of  the  muscles  which  squeeze 
and  compress  the  veins  and  drive  the  blood  to  the  next 
valve,  where  the  same  process  is  repeated. 

Circulation  Time. — The  circulation  time  can  not  be 
definitely  stated.  The  usual  estimate  is  that  from  twen- 
ty-five to  thirty  beats  of  the  heart  are  required  to  com- 
plete the  circulation ;  i.e.,  to  drive  the  blood  throughout 
the  body.  About  a  fourth  of  this  number  completes  the 
pulmonary  circulation.  The  velocity  through  different 
vessels  also  varies  as  does  the  quantity  supplied  to  each 


.  6  — The  aorta  and  its  branches. 


CIRCULATION  29 

organ.  The  latter  lias  been  determined  by  experiments 
which  prove  that  in  every  minute  each  hundred  grams 
of  the  leg  receive  5  c.c.  of  blood ;  while  the  same  weight 
of  spleen  would  receive  58  c.c.,  of  brain  136  c.c.  and  of 
the  thyroid  no  less  than  560  c.c.  in  the  same  time. 

Circulation  Velocity. — Circulation  velocity  does  not 
refer  to  the  rapidity  of  flow  through  any  given  vessel, 
but  to  the  time  it  takes  for  a  given  portion  of  blood  to 
pass  between  two  points  as  from  one  jugular  vein 
through  the  heart,  pulmonary  artery,  veins,  left  heart, 
aorta  and  capillaries  of  the  head  to  the  opposite  jugular. 
This  is  determined  by  putting  some  methyleiie  blue  in 
one  jugular  and  watching  for  its  appearance  in  the 
other.  This  has  been  accurately  determined  in  many 
lower  animals  and  is  estimated  to  be  about  thirty-two 
seconds  in  man.  As  the  rate  of  flow  is  much  more  rapid 
in  the  largest  than  in  the  smallest  arteries,  in  the  arteries 
than  in  the  capillaries,  and  in  the  veins  than  in  the  capil- 
laries, it  can  not  be  calculated  by  simply  watching  the 
speed  with  which  corpuscles  pass  through  one  of  the 
vessels.  Of  course  the  velocity  of  the  blood  current  will 
not  be  confounded  with  the  rate  of  the  pulse,  which  is 
an  impact  rather  than  a  current. 

The  Pulse. — The  pulse  is  seen  and  normally  felt  only 
in  the  arteries.  The  capillary  and  venous  systems  are  so 
much  wider  than  the  arterial,  that  the  force  of  the  heart- 
beat is  not  displayed  in  the  pulsatile  or  expansile  man- 
ner so  characteristic  of  the  latter.  The  column  of  blood 
extending  from  the  heart  throughout  the  arteries  may 
be  compared  to  a  series  of  balls  suspended  by  strings 
and  each  touching  the  other.  If  the  first  of  the  series 
is  struck  sharply  the  power  will  be  transmitted  through- 
out the  series,  but  it  will  visibly  affect  the  last  only.  If 
fresh  blood  is  pumped  into  the  aorta,  that  particular 


30  PHYSIOLOGY  FOR  NURSES 

blood  will  immediately  flow  but  a  short  distance,  but 
the  force  will  be  applied  to  every  drop  of  blood  in  every 
artery.  Each  artery  will  expand  and  contract  just  as 
the  aorta  does  and  the  expansion  will  be  synchronous 
with  the  heartbeat;  but  that  particular  jet  of  blood  will 
not  reach  the  artery  being  felt  for  several  seconds.  It 
follows  from  this  that  the  greater  the  power  of  the 
heartbeat  the  stronger  will  be  the  pulse;  the  more  fre- 
quent the  heartbeat,  the  more  rapid  the  pulse,  the  more 
the  capillaries  are  expanded,  the  less  the  resistance  to 
the  outflow,  the  more  compressible  the  pulse  and  the 
lower  the  blood  pressure. 

In  the  lungs  the  blood  circulates  under  the  same  gen- 
eral conditions  as  in  other  parts  of  the  body.  Pressure 
is  less  in  the  pulmonary  vessels  because  the  right  ventri- 
cle is  weaker  than  the  left.  Inspiration  and  expiration 
also  affect  both  the  systemic  and  pulmonary  circulation. 
In  inspiration  about  one-twelfth  of  all  the  blood  in  the 
body  is  in  the  lungs,  while  expiration  reduces  this  to 
one-fifteenth  or  eighteenth. 

Blood  Pressure. — If  liquid  be  pumped  into  an  inelas- 
tic tube,  the  pressure  will  be  exactly  proportionate  to 
the  quantity  of  fluid  and  the  force  of  the  pump.  As  soon 
as  the  pump  ceases  to  act,  the  pressure  falls  to  zero.  If 
the  same  experiment  be  conducted  with  an  elastic  tube 
pressure  will  again  be  equal  to  force  and  quantity,  but 
the  elastic  recoil  of  the  tube  will  maintain  some  pressure 
after  the  pump  ceases  to  act.  If  the  tube  be  converted 
into  two  whose  combined  area  is  as  great  as  that  of  the 
single  tube,  but  with  thinner  walls,  pressure  will  de- 
crease because  friction  will  be  greater ;  and  if  the  proc- 
ess of  division  be  continued  until  each  tube  is  of  micro- 
scopic size,  but  their  combined  area  is  much  greater  than 
that  of  the  original  tube,  pressure  will  be  very  greally 


CIRCULATION  31 

diminished.  If  now  several  small  tubes  unite  to  form  one, 
and  this  is  joined  by  another  formed  in  the  same  way  and 
the  process  is  repeated  until  there  is  but  one  tube,  the 
pressure  in  that  will  be  less  than  the  pressure  in  the 
numerous  microscopic  tubes,  and  much  lower  than  it 
was  in  the  one  large  elastic  tube  because  friction  so 


Fig.  7. — Apparatus  for  measuring  the  arterial  blood  pressure  in  man.  The 
pressure  in  the  cuff  is  raised  by  means  of  the  syringe  until  the  pulse  can 
no  longer  be  felt  at  the  wrist.  This  pressure  is  read  off  on  the  mercury 
manometer  (systolic  pressure).  (Pearce-Macleod,  Fundamentals  of  Hitman 
Physiology.) 

retards  the  flow  that  the  larger  tube  can  never  be  filled. 
The  arteries,  capillaries,  and  veins  form  such  a  set  of 
tubes  and  blood  pressure  varies  in  these  sets  of  vessels. 


32  PHYSIOLOGY   FOR   NURSES 

As  ordinarily  understood  blood  pressure  means  arterial 
pressure  and  is  taken  during  systole,  systolic  pressure 
or,  during  diastole,  diastolic  pressure.  The  method  of 
determining  pressure  is  to  encircle  the  arm  (because 
there  is  but  one  bone  and  the  muscles,  when  compressed, 
squeeze  the  arteries  uniformly)  with  a  long  rubber  sac, 
enclosed  in  leather,  which  is  connected  by  tubing  Avith 
a  column  of  mercury  and  an  air  pump.  "When  air  is 
pumped  into  the  sac  until  the  blood  can  no  longer  pass 
under  it,  as  shown  by  disappearance  of  the  radial  pulse, 
the  height  of  the  column  of  mercury  is  read.  This  is 
systolic  pressure  and,  in  healthy  young  men,  varies  be- 
tween 110  and  130  mm.  of  mercury. 

Pressure  Forces. — Pressure  forces  are  three  in  num- 
ber: i.e.,  the  power  of  the  heart,  the  resistance  ot  the 
vessels,  and  the  quantity  of  blood.  In  normal  animals, 
the  two  former  change  with  changing  conditions,  so 
that  a  practically  constant  level  of  pressure  is  main- 
tained the  greater  part  of  the  time.  Decrease  in  the  vol- 
ume of  the  blood  tends  to  lower  the  pressure,  but,  within 
certain  limits,  this  is  compensated  for  by  increase  in  the 
rate  of  the  heart  and  a  constriction  of  the  vessels.  Like- 
wise, if  fluid  is  introduced  into  the  vessels,  it  does  not 
cause  a  marked  and  persistent  rise  in  the  pressure,  due 
to  the  same  factors  working  in  the  opposite  direction. 
The  volume  of  the  blood  remaining  the  same,  certain 
drugs  are  capable  of  causing  vascular  contraction,  as 
epinephrine,  which,  uninterfered  with,  would  cause  an 
enormous  rise  in  pressure.  Injecting  this  drug  into  the 
circulation  does  cause  a  rise  in  the  pressure,  but  when 
this  reaches  a  certain  level,  the  heart  is  slowed,  in  or- 
der to  prevent  an  undue  strain.  On  the  other  hand, 
when  the  vessels  are  caused  to  dilate  by  nitrites,  the 


CIRCULATION  33 

heart,  beats  more  rapidly  in  the  attempt  to  raise  the 
pressure  back  to  the  normal  level. 

Occasionally,  this  compensatory  action  fails.  Such  is 
the  case  in  fainting  or  syncope.  Here,  the  vessels,  es- 
pecially in  the  abdominal  region,  dilate,  and  insufficient 
pressure  is  maintained  to  supply  the  brain  properly  with 
blood,  so  unconsciousness  occurs.  In  moderate  hemor- 
rhage, the  loss  of  blood  is  compensated  for  in  the  man- 
ner described,  but  when  the  loss  has  assumed  very  se- 
rious proportions,  the  pressure  falls  and  unconsciousness 
results.  It  is  obvious  that  this  fall  of  pressure  is  con- 
servative ;  if  it  did  not  take  place,  great  difficulty  would 
occur  in  regard  to  clotting.  Therefore,  it  may  be  un- 
wise to  resort  to  measures  aimed  to  raise  the  blood  pres- 
sure before  the  bleeding  point  has  been  located  and  the 
hemorrhage  checked. 

Diseases  which  harden  the  walls  of  small  vessels,  con- 
verting them  into  inelastic  tubes,  have  the  effect  of  con- 
stricting vessels,  increasing  resistance  and  raising  blood 
pressure.  Many  drugs  affect  blood  pressure  either,  like 
digitalis,  increasing  the  power  of  the  heart,  or,  like  the 
nitrites  (amyl,  sodium,  etc.)  by  dilating  peripheral 
vessels  and  causing  a  fall  of  blood  pressure.  Others  act 
upon  the  nervous  mechanism  of  the  heart,  which, 
roughly,  consists  of  a  set  of  sympathetic  fibers  which 
accelerate  or  augment  the  action  of  the  heart  and  a  set 
of  vagus  or  pneumo gastric  fibers  which  slow  or  inhibit 
its  action.  This  subject  will  be  discussed  under  the 
nervous  system. 


CHAPTER  II 

RESPIRATION 

The  air  which  surrounds  us  is  in  the  main  composed 
of  two  gases,  oxygen  and  nitrogen,  thoroughly  mixed 
but  not  chemically  combined.  Of  these  the  nitrogen  is 
inert  while  the  oxygen  is  essential  to  animal  life.  The 
organ  which  enables  us  to  bring  this  gas  in  contact  with 
the  blood  is  the  lung,  while  its  use  in  the  animal  econ- 
omy is  called  respiration.  But  taking  oxygen  into  the 
lungs,  would  be  of  no  service  if  the  process  stopped 
there.  It  is,  therefore,  carried  by  the  blood  into  all 
parts  of  the  body  where  the  oxygen  is  used  and  inju- 
rious matter  taken  up  and  removed.  If  two  gases  be 
placed  one  on  either  side  of  a  wet  membrane,  like  parch- 
ment, they  will  mix  with  each  other  by  a  process  called 
osmosis.  If,  therefore,  a  liquid,  like  blood,  containing 
oxygen  be  brought  in  contact  with  tissues  containing 
carbon  dioxide,  the  two  gases  would  interchange  even  if 
there  were  no  chemical  activity  to  promote  the  change. 
Blood  going  to  all  parts  of  the  body  carries  oxygen  in 
combination  with  hemoglobin.  When  in  contact  with 
live  tissue  this  oxygen  is  given  up  to  the  tissue  and  car- 
bon dioxide  is  taken  up  and  carried  by  the  venous  blood 
to  the  lungs  where,  in  the  cells  of  those  organs,  a  re-ex- 
change is  effected,  the  carbon  dioxide  being  given  up 
and  oxygen,  derived  from  the  inspired  air,  takes  its 
place.  The  last  exchange  is  called  the  external  and  the 
first  the  internal  respiration. 

The  organs  of  respiration  are  the  nose,  pharynx, 
larynx,  trachea  and  lungs.  Except  the  last,  and  in  all 

34 


RESPIRATION 


35 


but  the  ultimate  air  cells  of  the  lungs,  these  organs 
are  but  variously  modified  tubes  through  which  the  air 
is  drawn,  heated  and  moistened.  It  is  in  the  air  cells  that 
the  thin  Avails  of  the  pulmonary  capillaries  bring  the 
blood  close  enough  to  the  inspired  air  for  the  exchange 
to  take  place. 

Respiratory  Forces. — For  normal  respiration  the  re- 
spiratory forces  are  the  diaphragm  and  certain  muscles 


Fig.  8. — The  position  of  the  lungs  in  the  thorax.      (T.   Wingate  Todd.) 
(Pearce-Macleod,  Fundamentals  of  Human  Physiology.) 

which  move  the  ribs.  Essentially  the  lungs  are  a  pair 
of  elastic  bags,  communicating  with  atmospheric  air 
through  the  breathing  tubes,  enclosed  in  a  movable  bony 
framework  which  is  covered  by  soft  tissues  and  lined, 
for  each  lung,  by  a  frictionless  membrane  completely 
air-tight.  If  the  framework  increases  in  size,  the  lungs 
must  either  follow  it  or  leave  a  vacuum  between  lung 


•°>f>  PHYSIOLOGY    FOR    NURSKS 

and  frame.  Aii  increase  in  the  si/c  of  tlie  thorax,  there- 
fore, makes  the  air  pressure  in  the  lungs  less  than  the 
pressure  of  the  atmosphere  and  air  enters  the  lungs  un- 
til the  pressure  is  equalized.  Forced  inspiration  means 
simply  forced  increase  in  the  size  of  the  thorax  requir- 
ing a  corresponding  amount  of  air  to  establish  equilib- 
rium. The  ribs  slope  downward  and  forward  and  are 
fixed  behind.  Consequently,  when  the  anterior  end  is 
pulled  upward  they  must  push  the  sternum  forward  and 
increase  the  diameter  of  the  chest  from  before  back- 
wards.  At  the  same  time  the  spaces  between  them  in- 


Fig.   9. — Diagram   of  structure  of  lungs   showing  larynx,   bronchi,   bronchioles, 
and   alveoli.      (Pearce-Macleod,   Fundamentals   of  Unman   Physiology.) 

crease  and  the  chest  grows  from  above  downwards.  If, 
now,  the  diaphragm,  which  is  fastened  around  the  bar- 
rel-like chest,  convex  upwards,  contracts,  it  must  flatten 
the  dome  and  greatly  increase  the  space  within  the 
thorax.  It  must  be  borne  in  mind  that  this  space  con- 
tains not  only  the  heart  and  lungs,  but  the  great  vessels, 
and  that  the  force  which  causes  inrush  of  air  can  not  but 
produce  some  suction  (aspiration)  which  will  influence 
their  contents.  As  soon  as  the  inspiratory  muscles 
cease  to  act,  the  abdominal  contents,  resting  against  the 
under  surface  of  the  diaphragm,  and  held  in  place  by 


RESPIRATION  37 

the  powerful  and  elastic  muscles  of  the  abdominal  wall, 
begin  to  press  on  the  diaphragm  and  force  it  to  resume 
its  dome  shape.  The  ribs  drop  back  into  their  position 
of  rest,  the  elastic  lungs  contract  and  drive  out  the  air 
and  thorax,  diaphragm  and  lungs  are  ready  to  repeat 
the  act  of  inspiration.  The  descent  of  the  diaphragm 
pushes  the  abdominal  viscera  downwards  and  forward 
and  this  movement  communicated  to  the  abdominal 
wall  gives  its  name  to  this  type  of  breathing,  abdominal, 
which  is  most  noticed  in  children.  When  the  lower  ribs 
only  move  the  type  is  said  to  be  inferior  costal;  when 
the  clavicles  and  upper  ribs  move  the  type  is  superior 
costal.  The  latter  is  characteristic  of  civilized  women 
and  is  a  possible  provision  for  pregnancy,  though  many 
observations  indicate  improper  dress  as  a  cause  of  this 
type  of  inspiration. 

In  forced  inspiration,  as  in  asthma,  other  muscles  are 
brought  into  play.  The  same  is  true  of  forced  expi- 
ration where  the  abdominal  muscles  play  a  large  part. 

Respiratory  Cycle. — This  consists  of  two  parts,  the  in- 
take of  air,  inspiration,  and  the  output  or  expiration. 
Inspiration  takes  a  slightly  shorter  time  than  expiration, 
the  average  difference  being  the  proportion  of  five  to 
six;  though  in  children,  women,  and  the  aged  the  pro- 
portion may  be  six  to  eight  or  even  nine.  There  is  a 
slight  pause  after  expiration. 

Respiratory  Sounds. — If  the  ear  be  applied  to  the 
chest  during  inspiration  a  soft  murmur,  like  the  rust- 
ling of  leaves  in  a  gentle  wind,  is  heard,  followed,  dur- 
ing expiration,  by  a  similar  sound  during  a  shorter 
lime.  Note  the  apparent  contradiction:  The  time  of 
inspiration  is  shorter  than  that  of  expiration,  but  the  in- 
spiratory  sound  lasts  three  times  as  long  as  the  expir- 
atory. Both  sounds  seem  to  be  caused  by  the  friction  of 


38  PHYSIOLOGY   FOR   NURSES 

air  entering  and  leaving  the  infundibula  and  alveoli.  If 
the  air  vesicles  are  filled  up,  or  the  listening  is  done 
over  large  bronchi,  the  second  is  modified  and  becomes 
tubular.  It  is  the  difference  in  sound  caused  by  the  air 
moving  in  small  tubes  and  large  ones. 

Quantity  of  Air.— The  total  quantity  of  movable  air 
in  the  lungs  of  an  average  man  is  about  230  cubic  inches. 
Of  this  amount  about  20  cubic  inches  is  taken  in  at  each 
inspiration,  about  110  cubic  inches  can  be  taken  in  after 
an  ordinary  inspiration  and  about  100  cubic  inches  is 
the  amount  which  can  be  forcibly  expelled  after  an  or- 
dinary expiration.  The  amount  passing  in  and  out  in 
each  ordinary  respiratory  cycle  is  called  tidal  air,  that 
taken  in  by  forced  inspiration,  complemental  air  and 
that  which  can  be  expelled  by  the  greatest  effort  supple- 
mental. Tidal,  complemental,  and  supplemental  air  to- 
gether constitute  one's  vital  capacity. 

Not  the  utmost  effort  will  expel  all  the  air  from  lungs 
which  have  once  been  filled,  a  fact  which  causes  lung 
tissue  to  float  in  water,  which  no  other  tissue  will  do. 
The  fact  that  once  filled  lung  tissue  floats  and  that  never 
filled  sinks,  often  enables  experts  to  determine  whether 
a  dead  child  has  ever  breathed  or  was  born  dead.  The 
air  remaining  after  fullest  expiration  is  termed  residual 
air  and  amounts  to  about  100  cubic  inches. 

Number  of  Respirations. — Within  the  limits  of  health 
respirations  may  vary  from  sixteen  to  twenty-four  per 
minute,  or  one  respiration  to  four  heartbeats.  In  child- 
hood breathing  is  more  rapid  and  at  all  ages  it  varies 
with  exercise  or  the  position  of  the  body,  while  in  feb- 
rile diseases  the  rate  greatly  increases.  Some  patho- 
logic conditions  diminish  the  rate. 

Modifications  of  Respiration. — When  breathing  is  dif- 
ficult for  any  reason  it  is  termed  dyspnea,  from  two 


RESPIRATION  39 

Greek  words  signifying  "bad  breathing;"  when  it  is 
totally  arrested,  the  condition  is  called  asphyxia  and 
when  there  is  an  excess  of  oxygen  or  too  little  carbon 
dioxide  in  the  blood,  so  that  respiration  can  be  sus- 
pended without  injury,  a  condition  of  apnea  exists. 

Modifications  of  respiration  are  seen  in  sighing,  yawn- 
ing, laughing  and  sobbing,  snoring,  hiccoughing  and 
coughing. 

Sighing  is  a  slow,  large  inspiration,  followed  by  an 
audible  rapid  expiration. 

Yawning  is  practically  an  involuntary  sigh  accom- 
panied by  a  widely  opened  mouth.  It  may  be  caused 
by  stomach  pain  (hunger)  as  well  as  the  torpor  which 
precedes  sleep. 

Hiccough  is  a  spasmodic  contraction  of  the  diaphragm 
accompanied  by  closure  of  the  glottis.  It  is  often  patho- 
logic and  uncontrollable. 

Coughing  is  a  reflex  act  caused  by  irritation  of  the 
nerves  of  the  larynx.  The  mechanism  of  the  act  is  a 
full  inspiration  followed  by  a  sudden  strong  expiration. 

Laughing  and  sobbing  are,  mechanically,  identical. 
The  diaphragm  is  the  muscle  employed  in  each  act  and 
the  face  is  the  organ  of  expression. 

Snoring  is  the  vibration  of  the  soft  palate. 

CHEMISTRY  OF  RESPIRATION 

If  two  or  more  gases  are  confined  in  the  same  vessel 
they  will  mix  or  diffuse  throughout  the  space.  If  water 
or  other  fluid  be  in  the  space,  some  of  each  gas  will  en- 
ter the  fluid,  or  be  dissolved  in  it;  and,  under  some  con- 
ditions, some  of  the  gases  may  enter  into  chemical  com- 
bination with  the  liquid.  The  amount  of  gas  dissolved 
;ni (I  the  amount  in  combination,  will  vary  somewhat 


40  PHYSIOLOGY   FOR   NURSES 

with  the  pressure  applied.  As  the  essential  function  of 
the  respiratory  act  is  to  convey  one  gas  to  the  tissues 
and  another  away;  and  as  experiments  prove  that  some 
of  the  gas  is  in  solution,  but  most  of  it  in  combination, 
there  must  be  pressure  changes,  or  differences,  in  the 
lungs  and  in  the  tissues  to  facilitate  the  exchange. 

If  the  tidal  air  is  analyzed  we  shall  find  that  inspired 
rich  in  oxygen  and  that  expired  rich  in  carbon  dioxide. 
The  reserved  air  must,  therefore,  contain  a  larger 
amount  of  C02  than  the  complemental.  Now  as  tidal 
air  enters  the  alveoli  and  finds  them  filled  with  air  con- 
taining a  high  percentage  of  C02,  there  must  be  a  dif- 
fusion or  mixing  of  air  in  the  alveoli.  This  process  of 
mixing  goes  on  at  all  times. 

When  arterial  blood  passes  to  the  tissues  it  finds  them 
filled  with  C02  existing  under  a  pressure  which  causes 
it  to  enter  into  chemical  combination  as  well  as  solution. 
The  oxygen  in  the  arterial  blood,  chiefly  in  combination 
with  hemoglobin,  finds  the  pressure  lowered  as  soon  as  it 
reaches  the  tissues.  Pressure  on  the  oxygen  being  low,  it 
escapes  into  the  tissues ;  that  on  C02  being  high,  it  com- 
bines with  the  blood.  Upon  reaching  the  lungs  the  re- 
verse of  this  action  takes  place,  venous  blood  giving  up 
its  C02  and  taking  oxygen  instead  because  the  air  in  the 
alveoli  is  rich  in  oxygen  and  poor  in  C02,  while  the 
blood  is  rich  in  C02  and  poor  in  oxygen,  the  tendency 
being  for  oxygen  to  escape  from  the  alveoli  and  C02  to 
escape  from  the  blood  into  the  alveoli  until  the  pressure 
on  each  gas  is  equalized. 

Oxygen  and  carbon  dioxide  are  the  chief,  but  not  the 
only,  gases  inhaled  and  exhaled.  Atmospheric  air  con- 
tains, in  a  hundred  parts,  approximately  79  parts  of  ni- 
trogen, 20.96  parts  of  oxygen,  .04  parts  of  carbon  diox- 
ide and  minute  quantities  of  other  gases  with  about  1 


RESPIRATION  41 

per  cent  of  water.  Nitrogen  has  no  injurious  effect,  ex- 
cept by  excluding  oxygen.  Like  all  nonpoisonous  gases 
it  may  cause  asphyxia  if  breathed  pure,  but  would  cause 
it  no  more  quickly  than  lack  of  oxygen  if  the  nitrogen 
were  absent.  Carbon  dioxide  is  poisonous,  but  less  fatal 
than  carbon  monoxide  which  acts  by  combining  with  the 
hemoglobin  of  the  blood  and  excluding  oxygen,  because 
its  compound  with  hemoglobin  is  much  more  stable  than 
that  of  oxygen.  The  injurious  effects  of  rarefied  air, 
like  that  on  high  mountains,  is  due  to  lack  of  oxygen  in 
the  blood. 

Ventilation. — Briefly  stated  the  problem  of  venti- 
lation is  to  maintain,  in  a  closed  space  like  a  room,  the 
nearest  possible  approximation  to  atmospheric  condi- 
tions. The  problem  would  be  simple  if  it  were  not  for 
the  necessity  of  heating.  A  healthy  adult  gives  off  about 
six-tenths  of  a  foot  of  C02  per  hour,  that  is  he  changes 
the  contents  of  a  hundred  feet  of  air  from  four-tenths 
to  one  foot  of  C02.  If  this  process  be  carried  too  far,  he 
will  not  only  increase  the  actual  C02  but,  by  using  up 
the  oxygen,  still  more  increase  the  relative  content.  If 
a  supply  of  1,000  cubic  feet  of  fresh  air  is  furnished  per 
hour  for  each  well  person,  the  room  is  sufficiently  ven- 
tilated ;  but  in  hospitals  the  amount  required  is  3,000 
cubic  feet. 

Nervous  Mechanism. — Nervous  mechanism  is  almost 
automatic.  A  center  to  control  respiration  is  located  in 
the  medulla.  The  normal  stimulus  to  which  it  responds 
is  carbon  dioxide.  When  the  venous  blood  is  sufficiently 
charged  with  that  gas,  the  center  sends  a  message,  which 
is  carried  by  the  nerves  to  the  muscles  of  inspiration 
which  contract  and  cause  an  inrush  of  air.  If  there  be 
an  impediment  to  the  intake,  accessory  muscles  of  in- 
spiration are  called  upon  until  the  obstacle  is  overcome. 


42  PHYSIOLOGY   FOR   NURSES 

If  part  of  the  lung  is  occupied  by  a  foreign  substance, 
as  in  pneumonia,  the  respiratory  efforts  are  made  more 
frequently  because  there  is  more  C02  in  the  blood  and 
the  center  is  stimulated  to  greater  activity.  If  there  is 
too  little  C02,  the  center  is  less  excited  and  the  number 
of  inspirations  per  minute  will  decrease,  to  rise  again 
as  soon  as  the  proper  amount  of  C02  is  restored. 


CHAPTER  III 

FOOD  AND  DIGESTION 

Digestion  is  the  process  by  which  physical  and  chem- 
ical alterations  of  foodstuffs,  which  fit  them  for  absorp- 
tion, are  effected.  Animal  and  vegetable  tissues  contain 
foodstuffs  of  the  same  chemical  composition;  but  some 
animals  can  not  convert  certain  forms  of  vegetable  mat- 
ter into  food,  while  others  can.  When  an  animal  feeds 
upon  other  animals  it  is  called  carnivorous  and  feeds 
upon  tissues  similar  to  its  own.  When  it  feeds  upon 
vegetables  it  is  called  herbivorous  and  feeds  upon  tis- 
sues containing  the  same  chemical  elements  but  so  ar- 
ranged as  to  be  not  easily  digested  by  carnivorous  ani- 
mals. With  the  aid  of  light,  heat  and  moisture,  vege- 
tables take  up  chemical  elements  from  air  and  soil  and 
combine  them  into  the  proper  constituents  of  food  for 
herbivorous  animals,  and  these  in  turn,  convert  them  into 
the  similar,  but  more  digestible  foodstuffs  required  by 
man. 

Of  the  elements  of  the  chemist,  only  about  twenty  en- 
ter into  the  composition  of  our  tissues ;  and  of  these,  five 
form  so  much  of  our  bulk  that  the  others  may  be  men- 
tioned as  traces.  The  elements  which  chiefly  concern  us 
occur  as  follows,  in  every  hundred  parts : 

Carbon,  53 

Oxygen,  22 

Nitrogen,  16 

Hydrogen,  7 

Sulphur,  2 
43 


44  PHYSIOLOGY   FOR   NURSES 

The  various  constituents  of  the  body  may  be  divided 
into  two  great  classes,  organic  and  inorganic,  and  the 
first  into  those  which  contain  nitrogen  and  those  which 
do  not. 

The  Inorganic  constituents  are  water  and  the  various 
salts,  that  is  minerals  like  iron,  potash,  soda,  etc.,  in  com- 
bination with  some  acid. 

Water  is  the  most  widely  distributed  inorganic  mate- 
rial, constituting  more  than  half  the  body  weight.  It  is 
the  solvent  for  all  materials  which  are  carried  from  one 
part  of  the  body  to  another  for  its  nourishment  or  to  re- 
move the  worn-out,  useless  or  injurious  substances  which 
result  from  our  life  processes.  We  get  water  by  drink- 
ing it  in  the  form  of  water,  milk,  tea  or  coffee,  soups, 
etc. ;  but  a  small  portion  is  made  in  the  body  by  burning 
up  hydrogen. 

Salts  are  combinations  of  soda  and  lime  with  hydro- 
chloric or  some  other  acid  and  of  soda,  potash,  lime  and 
magnesium  with  phosphoric  acid.  In  the  first  case  we 
have  chlorates  or  chlorides  of  soda,  lime,  etc. ;  and  in  the 
latter,  phosphates  of  potash,  magnesium,  etc. 

The  most  important  and  widely  distributed  of  the  salts 
is  the  one  with  which  we  are  most  familiar,  chloride  of 
soda,  or  common  table  salt.  Phosphate  of  lime  is  a  nec- 
essary element  of  bone  and  iron  is  an  indispensable  ele- 
ment of  hemoglobin. 

Organic  Compounds  consist  of  nitrogenous  com- 
pounds which  are  subdivided  into  proteins,  like  the  red 
flesh  of  animals,  white  of  eggs,  etc.;  albuminoids  like 
gelatin  and  some  bodies  of  simpler  composition,  like 
urea,  which  are  largely  for  excretion;  and  nonnitrog- 
<  nous  compounds  which  are  fats  (butter,  fat  meat 
etc.),  carbohydrates  (starch,  sugar)  and  certain  other 
organic  bodies  like  alcohol  not  so  widely  used  as  the 


FOOD   AND   DIGESTION  45 

preceding.  Translated  into  simple  language  this  means 
that  we  require  for  health  lean  meat  (protein),  fat  meat, 
(hydrocarbon  or  fat)  and  vegetables  (starch  and  sugar), 
with  enough  water  to  dissolve  them  after  digestion  and 
carry  the  products  of  digestion  to  every  part  of  the 
body. 

Carbohydrates. — Carbohydrates  are,  chemically,  com- 
pounds of  carbon,  hydrogen  and  oxygen,  the  last  two 
occurring  in  the  proportions  found  in  water.  Thus  glu- 
cose (C6H1206)  is  composed  of  six  elements  of  carbon, 
twelve  of  hydrogen,  and  six  of  oxygen,  which  is  practi- 
cally the  same  as  saying  six  elements  of  carbon  in  three 
of  water,  which  is  composed  of  hydrogen  two  and  oxy- 
gen one  (H2'0).  There  are  various  types  of  carbohy- 
drates— glucose,  amylose — but  special  attention  need 
here  be  called  to  none  but  glycogen  which  is  the  pecul- 
iar form  of  starch  formed  in  animals. 

Fats  or  Lipoids,  are  found,  in  varying  amounts,  in  ani- 
mal tissues,  lying  under  the  skin  in  large  amounts,  be- 
tween the  muscles,  in  the  marrow  of  bones  and  in 
smaller  amounts  in  other  situations.  Fats,  in  the  form 
of  oils,  are  found  in  many  vegetables — olive,  cottonseed, 
nuts,  etc.  Chemically,  fats  are  compounds  of  glycerin 
and  a  fatty  acid.  They  are  insoluble  in  water,  and,  be- 
ing bad  conductors,  serve  to  keep  the  other  tissues 
warm.  Normal  fats  belong  to  one  of  three  types. 

Stearin,  solid  and  melting  only  at  comparatively  high 
temperatures.  Mutton  suet  is  a  fine  example  of  this  type. 

Palmitin,  is  the  principal  constituent  of  most  animal 
and  vegetable  fats.  It  melts  at  a  lower  temperature 
than  stearin. 

Olein,  always  fluid  except  in  low  temperatures,  is 
found  chiefly  in  vegetable  fats,  but  occurs  in  that  of 
animals. 


46  PHYSIOLOGY   FOR   NURsi.S 

Fats,  \vluMi  boiled  with  soda  or  potash,  break  up  into 
glycerin  and  fatty  acids,  which  latter  combine  with  soda 
or  potash  and  form  soap. 

If  fats,  soap  and  water  be  thoroughly  shaken  together 
the  fat  breaks  up  into  small  particles  which  are  held  in 
suspension  in  the  water  forming  an  emulsion.  Milk  is 
an  excellent  emulsion  whose  fat  gradually  rises  to  the 
top  in  the  form  of  cream. 

Nitrogenous  Bodies. — The  chief  constituents  of  mus- 
cles, glands,  nervous  tissue,  serum,  blood  and  lymph  are 
complex  bodies  called  proteins.  They  occur  in  vegeta- 
bles as  well  as  in  animals,  but  much  vegetable  protein 
is  indigestible  by  human  organs  and  comes  to  us  only 
after  furnishing  food  for  the  lower  animals.  Thus  peas 
and  beans  contain  23.7  per  cent  protein  as  compared 
Avith  22.7  in  fowls  and  20  per  cent  in  beef;  but  so  much 
of  the  protein  of  peas  is  unusable  by  the  human  diges- 
tive organs,  that  this  vegetable  can  not  be  used  as  a  sub- 
stitute for  meat.  Various  names  are  employed  to  desig- 
nate the  protein  derived  from  different  sources.  One 
found  in  milk  or  cheese  is  called  casein;  that  in  the  yolk 
of  eggs  vitellin  and  that  in  muscle  either  myosin,  or 
sj/ntonin. 

Not  all  bodies  which  contain  nitrogen  are  capable  of 
maintaining  health.  The  familiar  body  called  gelatin, 
derived  from  the  skin  and  connective  tissue,  contains  a 
considerable  proportion  of  nitrogen  and  yet  an  animal 
fed  upon  it  alone  will  starve  almost  as  quickly  as  one 
deprived  of  food  entirely.  This  seems  to  be  due  to  the 
absence  of  certain  amino  bodies  which  are  formed  of 
nitrogen  and  hydrogen  in  the  proportion  of  one  part  of 
N  to  two  of  H  or  NH2.  That  it  is  the  absence  of  these 
amino  bodies,  or  amino  acids,  which  keeps  gelatin 
from  maintaining  a  nitrogen  balance,  is  proved  by  feed- 


FOOD    AND    DIGESTION 


47 


the  animal  on  gelatin  plus  a  suitable  amount  of  an 
ammo  acid,  which  diet  maintains  health.  The  follow- 
ing tables  copied  from  Jones  and  Bunce  will  be  useful 
for  reference : 


COMPOSITION   Or   MILK 


HUMAN 


cow's 


Protein, 

70 
1.7 

7o 
3.5 

Butter  (fat), 

3.4 

3.7 

Lactose   (carbohydrate), 

6-2 

4.9 

Salts, 

0.2 

0.7 

COMPOSITION    OF 

EGGS 

% 

Total  solids, 

13.3 

Protein, 

12.2 

Sugar, 

0.5 

Fats,  lecithin,  cholesterin  (traces),  salts, 

0.6 

MEATS                                        OX 

CALF 

PIG 

FOWL 

PIKE 

Water,                            76.7 

75.6 

72.6 

70.8 

79.3 

Solids,                            23.3 

24.4 

27.4 

29.2 

20.7 

Proteins,                         20.0 

19-4 

19.6 

22.7 

18.3 

Fats,                                   1.5 

2.9 

6.2 

4.1 

0.7 

Carbohydrates,                0.6 

0.8 

0.6 

1.3 

0.9 

Salts,                                 1.2 

1.3 

1.1 

1.1 

0.8 

VEGETABLE 

FOODS                       WHEAT     BAPvLEY        OATS 

RICE 

PEAS      POTATOES 

Water,                        13.6 

13.8         12.4 

13.1 

14.8 

7o 

76.0 

Protein,                      12.4 

11.1         10.4 

7.9 

23.7 

2.0 

Fat,                               1.4 

2.2           5.2 

0.9 

1.6 

0.2 

Starch,                       67.9 

64.9         57.8 

76.5 

49.3 

20.6 

Cellulose,                     2.5 

5.3         11.2 

0.6 

7.5 

0-7 

Mineral  salts,             1.8 

2.7           3.0 

1.0 

3-1 

1.0 

Theoretically  peas  should  be  more  valuable  than  any 
other  vegetable,  particularly  the  potato,  because  they 


48  PHYSIOLOGY   FOR   NURSES 

are  rich  in  protein,  starch,  fat  and  salts;  while  the  po- 
tato is  poor,  comparatively,  in  everything  but  water. 
Practically  the  high  protein  value  of  the  pea  is  not 
available  while  its  large  percentage  of  indigestible  cel- 
lulose renders  it  objectionable  when  eaten  to  excess. 

DIGESTION 

That  digestion  is  chiefly  a  chemical  process  is  per- 
fectly true;  but  it  involves  a  process,  which  may  be 
called  vital  chemistry,  which  the  test  tube  has  not,  and 
may  not,  imitate  completely.  An  essential  part  of  di- 
gestion is  carried  out  by  bodies  called  enzymes  or  fer- 
ments. Another  is  the  production,  in  proper  proportion, 
of  the  acid  or  alkali  in  the  presence  of  which  alone 
these  ferments  will  act ;  while  yet  another  is  the  prepa- 
ration of  food,  by  chewing,  SAvallowing,  etc.,  and  its  agi- 
tation in  the  intestinal  canal  where  it  is  exposed  to  the 
ferments  on  the  one  hand  and  on  the  other  is  brought 
in  contact  with  the  vessels  by  which  the  products  of  di- 
gestion will  be  carried  into  the  body. 

The  Enzymes,  or  ferments  without  which  food  can- 
not be  digested,  are  of  three  chief  types:  (1)  amylo- 
lytic,  which  convert  starch  into  sugar;  (2)  fat  splitting, 
which  convert  fats  into  glycerin  and  fatty  acids;  and  (3) 
proteolytic,  or  those  which  convert  protein  into  simpler 
bodies. 

Besides  these  there  are  sugar  splitting  ferments  which 
change  the  nonabsorbable  into  absorbable  sugars,  and  a 
body  which  coagulates  protein,  as  in  the  change  of  milk 
to  clabber. 

The  ferments  which  act  on  starchy  foods  are  ptyalin, 
secreted  by  the  salivary  glands,  and  amylase,  formed  by 
the  pancreas. 


Transverse  colon — 1 


Ascending  colon — j 


FOOD   AND   DIGESTION 


I — Descending  colon 
! — Jejunum 


J?ig.   10. — Front    view    of    organs.      Semidiagrammatic. 


50  PHYSIOLOGY  FOR   NURSES 

The  fat  splitting  enzyme,  lipase,  or  steapsin,  is  formed 
by  the  pancreas. 

Proteolytic  ferments  are  pepsin,  formed  in  the  glands 
of  the  stomach  and  acting  only  in  the  presence  of  an 
acid,  and  trypsin,  formed  by  the  pancreas  and  acting  in 
an  alkaline  medium. 

Besides  these  well-known  ferments,  the  glands  in  the 
wall  of  the  small  intestines  furnish  various  enzymes 
which  act  upon  the  partly  digested  food  poured  into  the 
intestinal  canal  by  the  stomach.  Their  action  is  not  so 
well  understood  as  is  that  of  the  secretions  of  the  stom- 
ach and  pancreas. 

Before  considering  the  action  of  the  digestive  fer- 
ments, an  account  of  the  mechanics  of  the  alimentary 
canal  will  be  given. 

The  simplest  form  of  feeding  and  digesting  is  in  an 
unicellular  organ,  a  single  cell  of  protoplasm,  which 
wraps  itself  around  its  food  and  becomes,  in  its  entirety, 
a  chewing,  swallowing,  digesting,  absorbing  and  dis- 
charging organism.  In  man,  and  the  higher  animals,  af- 
ter food  has  been  procured,  the  successive  steps  are 
chewing  (mastication),  swallowing  (deglutition),  and  di- 
gestion. The  organs  concerned  are  the  mouth,  contain- 
ing the  teeth,  tongue,  and  salivary  gland;  the  pharynx 
and  esophagus,  the  swallowing  organs ;  the  stomach  and 
intestines  which  are  the  digesting,  absorbing  and  evacu- 
ating organs. 

Food  is  held  between  the  grinding  teeth  by  the  mus- 
cles of  the  cheek  (chiefly  the  buccinator)  on  the  outside 
and  the  tongue  between  the  teeth.  Here  it  is  not  only 
thoroughly  crushed,  but  is  mixed  with  the  saliva  which 
begins  the  digestion  of  starchy  food.  When  this  proc- 
ess is  completed,  the  larynx  is  pressed  up  under  the  hyoid 
bone  and  the  base  of  the  tongue,  the  top  of  which  organ, 


FOOD   AND   DIGESTION  51 

aided  by  the  mylohyoid  muscles,  crowds  the  food  against 
the  roof  of  the  mouth  and,  exerting  pressure  from  before 
backwards,  forces  the  food  under  the  soft  palate,  which 
it  drives  upward  to  protect  the  back  entrance  of  the  nos- 
trils, and  over  the  epiglottis,  which  is  pressed  down  over 
the  air  passage  (larynx)  and  the  food  is  driven  within 
the  grasp  of  the  pharynx  and  esophagus  over  which  a 
wave  of  contraction  passes  from  above  downward  until 
the  bolus  is  forced  into  the  stomach. 

Stomach  Movements.— The  walls  of  the  stomach,  when 
empty,  are  in  close  contact,  like  any  other  empty  bag. 
When  food  enters  it  separates  these  walls  only  in  pro- 
portion to  the  bulk  of  the  food,  and  closely  adheres  to 
them.  Hence,  when  the  next  mouthful  is  swallowed,  it 
does  not  come  into  direct  contact  with  the  stomach,  but 
with  the  coating  of  food  which  has  already  lined  that 
organ.  Successive  deposits  of  food  will  form  successive 
layers,  millers'  law  of  "first  come  first  served"  deter- 
mining the  order  of  digestion.  It  follows  that  the  hydro- 
chloric acid  of  the  stomach,  essential  to  the  action  of 
pepsin  but  fatal  to  that  of  ptyalin,  does  not  necessarily 
come  in  contact  with  any  but  the  first  food  swallowed; 
and  that  the  action  of  saliva  on  starch  may  continue  for 
an  indeterminate  time  in  the  stomach.  This  result  is 
further  promoted  by  the  peculiar  action  of  the  stomach 
muscle,  which  does  not  communicate  a  churning  move- 
ment to  all  the  food  contained  in  the  organ,  but  seems 
to  divide  into  two  sets  of  activity,  one  confined  to  the 
large  or  cardiac  end  of  the  stomach  and  the  other  to  the 
small,  pyloric,  extremity.  At  the  large  end  there  is  lit- 
tle muscular  action,  this  portion  of  the  organ  acting  as 
a  reservoir  for  the  undigested  food;  while,  about  the 
middle  of  the  stomach,  the  waves  of  contraction  start 
which  force  the  food  toward  the  pyloric  end,  mix  it  with 


52 


PHYSIOLOGY   FOR   NURSES 


the  gastric  juice  and  reduce  it  to  the  thin  liquid,  chyme, 
which  is  the  end  of  stomach  digestion.  Between  the  ad- 
mission of  food  to  the  stomach  and  the  appearance  of 
chyme  in  the  intestine,  several  hours  elapse.  During 
this  time  contraction  waves,  at  intervals  of  about  twenty 


SMALL 
INTESTINE 


ANUS 
Fig.   11. — Diagram  of  the  alimentary  tube  and  its  appendages.      (After  Testut.; 

seconds,  press  the  liquefying  food  against  the  pyloric 
valve,  which  does  not  yield  until  the  food  is  in  a  liquid 
form.  It  then  opens  and  the  liquid  part  escapes  into  the 


FOOD    AND    DIGESTION  53 

duodenum,  where  the  reaction  is  alkaline  and  where  in- 
testinal digestion  begins.  Finally  undigested  arid  indi- 
gestible articles  are  allowed  to  pass. 

Intestinal  Movements. — The  muscular  coats  of  the  in- 
testine are  arranged  in  two  layers,  an  outer  longitudinal 
and  an  inner  circular.  Obviously  if  each  band  of  circu- 
lar fibers  contracted  in  succession  a  wave  of  constriction 
would  finally  pass  over  the  entire  length  of  the  tube 
from  stomach  to  large  intestine;  and,  if  each  band  re- 
laxed directly  after  contraction,  there  would  be  an  in- 
active or  dilated  area  always  both  above  and  below  the 
wave  of  contraction — the  dilated  area  above  constantly 
increasing  and  the  one  below  decreasing  in  length.  This 
is  the  normal  or  peristaltic  movement  of  the  intestine. 
At  the  same  time  the  longitudinal  fibers  seem  to  con- 
tract and  draw  the  entire  tube  over  the  advancing  food. 
If,  from  disease  or  other  cause,  a  wave  can  be  excited 
below  and  made  to  pass  upwards,  the  contents  of  the  in- 
testine wrould  be  forced  into  the  stomach,  as  in  obstruc- 
tion of  the  bowel  when  fecal  vomiting  is  seen.  This  ac- 
tion is  termed  antiperistalsis.  There  seem  to  be  local 
constrictions  at  various  points,  in  addition  to  normal  peri- 
stalsis, which  serve  to  break  the  column  of  food  into 
many  segments  and  both  promote  mixing  with  the  in- 
testinal and  pancreatic  ferments  and  exposure  to  ab- 
sorptive channels. 

Nervous  Control. — Both  the  stomach  and  intestines  re- 
ceive nerve  fibers  through  the  vagi  (pneumogastric  or 
tenth  cranial  nerve)  and  the  sympathetic  system  of 
nerves. 

Movements  of  Large  Intestines. — The  opening  of  the 
small  intestine  into  the  large  is  guarded  by  the  ileocecal 
valve  and  by  a  sphincter  muscle,  normally  in  a  state  of 
contraction.  Food  passing  into  the  large  intestine  is 


54  PHYSIOLOGY   FOR   NURSES 

still  in  a  semifluid  state,  but  becomes  solid  about  the 
middle  of  the  transverse  colon.  Waves  of  contraction 
of  the  same  general  character  as  those  seen  in  the  small 
intestine  determine  the  onward  movement  in  the  large. 
There  seems  to  be  a  normal  antiperistaltic  Avave  from 
the  middle  of  the  transverse  colon  back  to  the  ileocecal 
valve  to  retard  movement  and  allow  longer  time  for  ab- 
sorption. Beyond  the  transverse  colon  we  can  properly 
speak  of  feces  instead  of  food.  The  material  continues  to 
lose  water  until  the  sigmoid  flexure  is  reacned.  This  is  a 
sort  of  reservoir  for  fecal  matter  where  it  remains  until 
just  before  defecation,  the  rectum  apparently  remain- 
ing empty  until  that  time. 

Defecation. — This  is  partly  a  voluntary  and  partly  an 
involuntary  act.  The  normal  stimulus  seems  to  be  the 
passing  of  fecal  matter  from  the  signioid  into  the  rec- 
tum. This  excites  the  center  for  defecation  in  the  lum- 
bar part  of  the  spinal  cord,  the  sphincters  of  the  rectum, 
only  partly  under  the  control  of  the  will,  are  relaxed, 
the  diaphragm  contracts  drawing  a  full  supply  ot  air 
into  the  lungs,  and  remains  fixed  while  the  abdominal 
muscles  contract  forcibly  and  force  out  the  contents  of 
the  bowel. 

Vomiting1, — Vomiting  is  the  ejection  of  the  contents 
of  the  stomach  through  the  esophagus  and  mouth.  The 
order  of  events  is,  a  feeling  of  nausea,  a  flow  of  saliva,  a 
contraction  of  the  stomach  from  the  middle  towards  the 
esophageal  opening,  descent  of  the  diaphragm  so  as  to 
press  on  the  stomach,  a  sudden  and  violent  contraction 
of  the  abdominal  muscles,  exerting  still  further  pres- 
sure on  the  stomach  whose  contents  are  forced  along  the 
esophagus  and  out  of  the  mouth.  As  the  soft  palate 
can  not  be  so  well  carried  over  the  posterior  nares  from 


FOOD   AND   DIGESTION  55 

behind,  these  cavities  are  often  unprotected  and  some  of 
the  ejected  matter  is  forced  into  them. 

Nervous  Mechanism. — The  nervous  mechanism  is  a 
very  complex  reflex  action.  A  vomiting  center  may  ex- 
ist in  the  medulla.  Many  sensory  nerves  may  be  con- 
cerned, particularly  those  connected  with  vision  and  equi- 
librium. Irritation  of  the  sensory  nerves  of  the  stomach 
is,  however,  the  most  constant  cause. 

Hunger  and  Thirst. — These  sensations  are  the  cry  of 
cells  throughout  the  body  for  food  and  drink,  with  a 
local  manifestation  in  the  stomach  and  throat.  The 
empty  stomach  contracts  at  irregular  intervals  and  these 
contractions  are  attended  by  slightly  painful  sensations, 
"hunger  pains,"  until  food  or  some  substitute  is  taken. 
Thirst  is  felt  whenever  the  total  amount  of  water  in  the 
body  falls  beloAV  a  certain  point.  It  occurs,  therefore, 
as  a  symptom  following  loss  of  blood,  perspiration  or  fre- 
quent urination.  The  sense  of  distress  is  felt  in  the 
pharynx  chiefly  and  is  transmitted  by  the  ninth  cranial 
(glossopharyngeal)  nerve. 

Action  of  Digestive  Secretions 

The  Salivary  Glands. — These  are  three  in  number, 
parotid,  much  the  largest,  situated  between  the  lower 
jaAv  and  the  base  of  the  skull;  submaxillary,  under  the 
body  of  the  lower  jaw,  and  the  sublingual,  just  under  the 
tongue.  The  mixed  secretion  of  these  glands  contains 
994  parts  of  water  and  only  six  parts  of  solid  material 
in  a  thousand  parts.  The  solids  are  some  salts  of  potash, 
soda  and  magnesia,  mucin  and  ptyalin. 

Nervous  Mechanism. — As  the  nervous  control  of  these 
glands  is  well  understood  and  is  very  similar  to  other 
complex  reflexes,  it  is  explained  at  some  length  as  an 
example.  The  simplest  form  of  reflex  arc  is  a  spot  in 


56 


PHYSIOLOGY   FOR   NURSES 


the  central  nervous  system  connected  by  at  least  two 
nerves  with  a  given  gland  or  other  structure.  On©  nerve 
conveys  impulses  from  center  to  organ  and  is  called  an 
efferent  nerve;  the  other  carrying  impulses  from  pe- 
riphery to  center,  is  called  an  afferent  nerve.  Thus  if  a 
little  salt  be  placed  on  the  tongue  a  message  is  sent  to 
the  center  which  controls  secretion  which  acknowledges 
it  by  sending  a  message  to  the  gland  cells  to  begin  se- 
cretion. Two  other  nerve  impulses,  however,  are 


Cardiac  Orifice 


(Esophagus 


Funclus 


Great  Curvature 


Ductus  Communis.- 
Choledochus 


—  Duct  of  Wirsung 


Duodenum 
Fig.  12. — The  stomach  and  duodenum  opened.     (Buchanan's  Anatomy.) 

needed  before  the  gland  can  function  properly — one  in- 
creasing and  one  decreasing  the  blood  supply.  These 
are  called  vasodilator  and  vasoconstrictor  fibers.  The 
function  of  the  first  is  to  increase  the  amount  of  blood 
on  which  the  gland  can  act.  Vasodilator  fibers  are  car- 
ried along  with  the  secretory  fibers  in  the  cranial  nerve 
called  chorda  tympani,  while  vasoconstrictor  fibers  come 
from  the  sympathetic.  Afferent  fibers  are  carried  by 


FOOD   AND   DIGESTION  57 

many  nerves,  chiefly  those  of  smell  and  taste,  stimula- 
tion of  which  will  excite  a  flow  of  saliva.  Dilatation  of 
the  blood  vessels  in  a  gland  will  produce  two  chief  ef- 
fects. First  it  brings  into  contact  with  the  gland  cells 
a  larger  quantity  of  blood  containing  the  material  from 
which  that  particular  secretion  is  made ;  and,  second  by 
increasing  the  pressure  it  will  force  a  larger  quantity  of 
the  watery  constituents  of  the  blood  through  the  vessel 
wall  and  into  the  glandular  structure.  There  are  thus 
two  distinct  acts,  filtration,  which  is  mechanical,  and  se- 
cretion, or  manufacture,  which  is  a  vital  function  per- 
formed by  living  tissue. 

Mouth  Digestion 

Saliva. — The  salivary  secretion  acts  mechanically  to 
moisten  dry  food,  thus  getting  it  into  a  suitable  condi- 
.tion  for  swallowing;  through  the  mucin  contained  to 
lubricate  the  mass,  and  by  the  ptyalin,  to  digest  some  of 
the  starch.  This  is  accomplished  by  causing  the  starch 
molecules  to  take  up  water,  in  chemical  combination, 
thus  converting  it  into  maltose  and  dextrine,  two  forms 
of  sugar  which  are  not  absorbed  as  such  but  have  to  be 
converted  into  dextrose  in  the  intestines.  Ptyalin  diges- 
tion, therefore,  is  simply  preparatory.  Food  is  retained 
in  the  mouth  for  too  short  a  time  to  be  digested,  but  re- 
cent evidence  shows  that  it  may  be  held  in  the  fundus 
of  the  stomach  for  more  than  an  hour  before  the  hydro- 
chloric acid  arrests  ptyalin  digestion. 

Stomach  Digestion 

Gastric  juice  is  secreted  by  glands  in  the  mucous  lin- 
ing of  the  stomach.  It  is  a  watery  solution  containing 
pepsin,  and  rennin,  the  first  to  act  on  proteins,  the  sec- 


58 


PHYSIOLOGY   FOR   NURSES 


ond  to  coagulate  the  albumin  of  milk.  In  addition  about 
five-tenths  of  one  per  cent  of  gastric  juice  is  hydro- 
chloric add,  a  strong  mineral  acid  which  promotes  the 
activity  of  pepsin. 

Mechanism  of  Secretion. — The  mere  smell  or  taste  of 
appetizing  food  is  enough  to  start  gastric  secretion  and, 
indeed,  seems  to  be  its  normal  stimulus.  Some  foods, 
however,  appear  to  contain  substances  called  secreto- 
gogucs,  which  continue  to  excite  secretion  after  intro- 
duction into  the  stomach.  Meat  extracts  and  juices  ap- 


Fig.  13. — Schema  of  simple  reflex  arc:  r,  receptor  in  an  epithelial  mem- 
brane; a,  afferent  fiber;  s,  synapsis;  c,  nerve  cell  of  center;  e,  efferent  fiber; 
in,  effector  organ.  (Pearce-Macleod,  Fundamentals  of  PI  it  man  Physiology.) 

pear  to  possess  these  substances  in  a  high  degree,  while 
they  seem  almost  absent  from  bread  and  white  of  egg 
and  present  in  but  small  quantity  in  milk. 

Pepsin  can  not  act  in  an  alkaline  solution  and  acts  best 
in  the  presence  of  hydrochloric  or  other  mineral  acid.  It 
acts  on  protein  alone  which  it  finally  converts  into  pep- 
tones, a  soluble  protein  more  ready  for  absorption  than 
pure  protein.  There  are  intermediate  steps  before  the 


FOOD   AND   DIGESTION  59 

peptones  appear.  First  the  protein  swells  up  and 
changes  into  an  acid  albumin  called  syntonin,  which 
passes  through  two  successive  stages — primary  and  sec- 
ondary proteoses — before  peptone  is  produced. 

Rennin  is  the  ferment  which  changes  milk  to  clabber. 
It  acts  well  in  the  presence  of  hydrochloric  acid.  Cow's 
milk  forms  a  solid  mass,  or  firm  clot,  not  unlike  the  clot 
of  blood  save  in  color,  which  squeezes  out  the  wliey  af- 
ter standing.  Human  milk  forms  a  loose  flocculent  clot, 
probably  more  easily  mixed  with  gastric  juice.  Rennin 
does  not  digest  the  casein,  which  is  digested  by  pepsin 
as  are  other  proteins.  The  clotting  is  probably  to  pre- 
vent the  immediate  passage  of  milk  into  the  duodenum 
before  stomach  digestion  could  begin.  There  seems  to 
be  no  other  food  substance  on  which  rennin  acts. 

The  stomach  has  no  power  of  digesting  starchy  foods 
which  leave  it  in  the  condition  in  which  mouth  digestion 
has  left  them.  Fats  are  not  appreciably  acted  upon  by 
the  gastric  ferment,  but  are  more  or  less  liquefied  and 
mixed  with  the  other  foods  in  the  chyme.  By  soaking 
into  and  around  particles  of  bread  or  other  food,  fats 
may  interfere  with  stomach  digestion. 

Stomach  digestion  is  more  preparatory  than  complete. 
Apparently  about  half  of  the  proteins  pass  into  the 
duodenum  as  either  peptones  or  proteoses,  20  per  cent  as 
unchanged  proteins  while  but  a  small  part  of  the  re- 
mainder is  absorbed  from  the  stomach.  Some  native 
proteins  are  not  acted  on  by  the  pancreatic  juice  and 
must  receive  preparatory  treatment  in  the  stomach. 
Mixing  the  foods,  warming  them,  separating  the  fats 
from  other  foods  with  which  they  are  mechanically 
mixed,  emulsifying  them,  partly  digesting  protein  and 
regulating  the  amount  poured  into  the  duodenum  seem 
the  chief  functions  of  the  stomach. 


60 


PHf  SIOLOGY   FOR   NURSES 


Absorption'  from  the  stomach  seems  to  be  slight,  even 
water  passing  into  the  duodenum  almost  at  once.  Al- 
cohol, however,  is  readily  and  rapidly  absorbed. 

Chyme  is  denned  as  "the  semiliquid  mass  of  partly 
digested  food  passed  from  the  stomach  into  the  duo- 
denum." It  contains:  (1)  digested  protein  in  the  form 
of  peptones  or  proteoses;  (2)  carbohydrates  which  have 
been  partly  digested  by  plyalin;  (3)  fat  warmed  and 


© 


Fig.    14. — Cross  section  of  pancreatic   tubule   (modified   from   Sabotta). 

mixed  in  an  emulsion  but  otherwise  not  appreciably 
changed;  (4)  undigested  proteins  and  carbohydrates; 
and  (5)  indigestible  substances  which  enter  the  duo- 
denum late  and  are  not  proper  constituents  of  chyme 
but  are  mixed  with  it. 

Pancreatic  and  Intestinal  Digestion 

The  product  of  stomach  digestion  meets,  in  the  in- 
testines, with  three   digestive    fluids;    i.e.,    pancreatic 


FOOD   AND   DIGESTION  61 

juice,  succus  entericus  (intestinal  juice)  and  bile.  The 
action  of  the  three  is  simultaneous,  but  a  separate  de- 
scription must  be  given  of  each  to  be  intelligible. 

Pancreatic  juice  contains  three  ferments,  trypsin, 
amylase  and  lipase  to  act  on  proteins,  carbohydrates 
and  fats.  The  pancreas  is  an  elongated  body  reaching 
from  the  hollow  of  the  duodenum  to  the  spleen  and  is 
a  compound  tubular  gland  like  the  salivary  glands. 
Its  secretion  is  poured  through  a  long  tube  (duct  of 
Wirsung)  which,  after  joining  the  common  bile  duct, 
opens  into  the  duodenum.  The  secretion  is  a  clear, 
watery  fluid  in  man,  very  abundant,  amounting  to  from 
500  to  800  c.c.  a  day.  The  nerve  supply  is  derived  from 
the  vagus  and  the  celiac  plexus.  The  secretion  appears 
to  begin  soon  after  food  is  placed  in  the  stomach  and 
continues  from  two  to  four  hours;  the  first  acid  chyme 
which  enters  the  duodenum  appears  to  incite  the  pan- 
creas to  activity.  This  activity  is  probably  not  pro- 
duced by  reflex  nerve  action,  but  by  the  production  of 
a  chemical  body,  secretin,  which  is  absorbed  by  the 
blood,  carried  to  the  pancreas  and  stimulates  the  organ. 
A  similar  explanation  is  given  of  the  secretion  of  gas- 
tric juice.  Bodies  which  are  thus  formed  and  act  in 
this  manner  are  termed  hormones.  The  character  of  the 
food  determines  the  type  of  the  secretion;  i.e.,  if  meats 
alone  are  eaten  the  juice  will  be  rich  in  trypsin ;  if  fats, 
in  lipase;  if  bread,  in  amylase. 

Trypsinogen  alone,  the  immediate  enzyme  of  the  pan- 
creas, is  not  able  to  act  on  proteins  but  requires  the 
presence  of  another  substance,  kinase  or  entcrokinase, 
which  is  formed  by. the  mucous  membrane  of  the  small 
intestine,  by  which  it  is  converted  into  trypsin. 

Trypsin  differs  from  pepsin  in  the  following  particu- 


62  PHYSIOLOGY  FOR  NURSES 

lars:  It  can  act  in  neutral,  slightly  acid  or  distinctly 
alkaline  solutions. 

Its  effect  on  proteins  is  not  only  more  powerful  but 
more  rapid  than  that  of  pepsin. 

It  breaks  up  the  protein  molecule  more  completely. 
The  joint  action  of  trypsin  and  pepsin  changes  the  com- 
plex structure  of  the  many  kinds  of  protein  into  simple 
bodies  of  the  ammo-acid  type  more  soluble  than  the 
original  form  and  prepares  them  for  the  action  of  erep- 
sin  (the  protein  enzyme  of  the  intestinal  juice)  which 
breaks  up  the  products  of  peptic  and  tryptic  digestion 
into  such  simple  forms  that  the  human  body  can  use 
them  as  building  stones  out  of  which  its  own  peculiar 
form  of  proteins  can  be  constructed. 

Amylase  acts  upon  starches  in  the  same  way  as 
ptyalin,  converting  them  into  maltose  and  achroodex- 
trin,  a  preparatory  step  to  their  final  conversion  into 
dextrose  by  the  maltose  of  the  intestinal  juice.  This 
digestion  is  completed  by  the  time  the  food  gets  to  the 
ileocecal  valve. 

Lipase  or  Steapsin  is  the  first  of  the  fat  splitting  fer- 
ments. This  ferment  splits  fats  into  glycerin  and  a 
fatty  acid  and  the  latter  combines  with  some  of  the  salts 
present  to  form  a  soap  which  is  used  to  hold  the  fats  in 
an  emulsion,  in  which  form  they  are  more  readily  acted 
on  by  the  lipase.  This  is  the  only  ferment  which  seems 
to  have  the  power  of  acting  in  either  direction;  i.e.,  it 
can  either  split  fats  or  it  can  take  the  component  parts 
(glycerin  and  fatty  acid)  and  combine  them  to  form 
fat.  Lipase  acts  best  in  the  presence  of  bile. 

Succus  entericus,  intestinal  juice  is  secreted  by  the 
tubular  glands,  crypts  of  Lieberkiihn,  Avhich  line  the 
intestinal  canal.  It  seems  to  act  only  on  starchy  foods ; 
but  there  are  several  enzymes  in  the  juice  which  can 


POOD   AND   DIGESTION  63 

be  extracted  from  the  mucous  membrane  of  the  intes- 
tines which  act  011  various  foods,  breaking  the  products 
of  gastric  and  intestinal  digestion  into  simpler  bodies, 
better  fitted  either  for  absorption  or  to  be  employed  as 
tissue  builders.  The  action  of  enterokinase,  erepsin  and 
secretin  have  been  alluded  to. 


Fig.  15. — Injected  lacteal  vessels  in  two  villi  of  human  intestine.  (Teich- 
mann.)  X  100.  I,acteals  filled  with  white  substance  and  blood  vessels 
with  dark. 

Bile  is  not  a  digestive  fluid,  but  it  so  largely  promotes 
the  splitting  and  absorption  of  fats  that  its  presence  as 
an  auxiliary  is  essential  to  health. 

Absorption  in  Small  Intestines 

Absorption  of  Proteins. — The  greater  part  of  digested 
proteins  is  absorbed  by  the  blood  vessels  of  the  intes- 


64  PHYSIOLOGY  FOR   NURSES 

tinal  villi.  This  is  proved  by  tying  the  thoracic  duct  so 
the  fluid  it  carries  can  not  get  into  the  blood.  Animals 
thus  treated  continue  to  absorb  and  utilize  proteins  as 
before.  The  actual  form  in  which  nitrogenous  foods 
enter  the  blood  current  is  that  of  the  ammo  acids,  which 
are  carried  to  the  various  tissues  which,  in  turn,  select 
such  acids  as  are  suitable  for  their  repair  or  upbuilding. 
Some  of  the  organs,  notably  the  liver,  have  the  power 
of  converting  these  acids  not  into  tissue  but  into  some 
other  nitrogenous  compound — urea  in  the  case  of  the 
liver. 

If  the  contents  of  the  small  intestine  be  examined  at 
the  ileocecal  valve,  it  will  be  found  that  from  97  to  99 
per  cent  of  such  foods  as  milk,  eggs  and  meats  have  been 
absorbed,  while  the  proportion  of  vegetable  protein 
absorbed  is  much  smaller — from  70  to  80  per  cent.  This 
seems  due  to  the  entanglement  of  the  vegetable  pro- 
teins in  indigestible  cellulose. 

Absorption  of  Carbohydrates. — Starchy  food  is  ab- 
sorbed as  simple  sugars.  Rather  more  than  a  pound 
(500  grams)  may  be  utilized  in  a  day,  all,  in  the  form 
of  dextrose,  is  stored  up  as  glycogen,  keeping  the 
amount  of  sugar  in  the  blood  constant  about  15  per  cent. 
When  excessive  amounts  of  starchy  food  or  sugar  are 
eaten,  the  liver  may  be,  for  the  time,  overworked  and 
sugar  may  temporarily  appear  in  the  urine. 

Absorption  of  Fats. — The  fatty  acids  and  glycerin  of 
intestinal  digestion  are  absorbed  as  such  and  appear, 
to  some  extent  at  any  rate,  to  be  recombined  in  the 
epithelial  cells  of  the  villi.  After  passing  the  epithelium 
the  fat  is  taken  up  by  the  lacteals  of  the  villi  and  carried 
by  the  thoracic  duct  to  the  beginning  of  the  left  in- 
nominate vein  where  it  is  poured  into  the  blood  stream. 
A  small  amount,  however,  appears  to  be  absorbed  directly 


FOOD   AND   DIGESTION  65 

by  blood  vessels  of  the  villi.  Different  fats  are  absorbed 
in  varying  degrees — of  olive  oil  nearly  98  per  cent  is 
absorbed  while  only  about  90  per  cent  of  mutton  fat  is 
so  accounted  for. 

Large  Intestine — Digestion  and  Absorption 

The  secretion  of  the  large  intestine  contains  no 
enzyme.  Hence,  such  digestion  as  occurs  in  that  area 
is  simply  a  continuation  of  activity  of  the  ferments  car- 
ried in  from  the  small  intestine.  Absorption,  particu- 
larly of  water,  does  take  place.  Water  is  absorbed  in 
the  small  intestine,  but  is  replaced  by  osmosis,  since  the 
contents  of  the  intestine  at  the  ileocecal  valve  are  as 
fluid  as  at  the  pylorus;  but,  there  being  no  such  com- 
pensation in  the  large  intestine,  fluid  is  rapidly  lost  and 
the  contents  quickly  attain  the  fecal  character.  The 
reaction  in  the  large  intestine,  as  in  the  small,  is  alka- 
line and  promotes  the  growth  of  bacteria,  particularly 
those  which  attack  protein.  Putrefaction,  therefore,  is 
a  normal  activity  in  the  large  intestine.  By  it  the  rem- 
nants of  proteins  are  split  into  end  products  some  of 
which  are  carried  off  in  the  feces,  others  in  the  urine. 
Some  of  these  products  may  be  injurious  if  absorbed  in 
the  blood,  explaining  some  of  the  ill  effects  of  constipa- 
tion. 

Composition  of  Feces. — The  amount  of  fecal  matter 
will  vary  with  the  amount  and  character  of  the  blood. 
When  meats  alone  are  used,  small  dark  colored  actions 
result.  If  the  diet  consists  largely  or  wholly  of  vege- 
tables, particularly  of  those  containing  much  cellulose 
or  woody  fiber,  the  amount  of  fecal  matter  will  increase 
in  amount  up  to  even  500  grams — a  little  more  than  a 
pound — as  compared  with  170  grams— about  a  third  of 
a  pound.  Fecal  matter  is  composed  of  indigestible 


66  PHYSIOLOGY   FOR    NURSES 

bodies,  seeds,  grains  of  corn,  ligaments;  undigested 
fragments  of  digestible  food;  some  results  of  intestinal 
secretion;  inorganic  salts,  mucus,  pigment,  the  results 
of  putrefaction,  etc. 

End  Results — Summary 

The  processes  of  digestion  are  merely  preparatory: 
the  food  is  reduced  by  these  processes  to  such  a  form 
that  it  may  be  absorbed.  Changes  fully  as  important 
take  place  after  the  food  has  left  the  alimentary  canal, 
constituting  what  is  known  as  "metabolism."  Unfor- 
tunately, our  knowledge  regarding  these  changes  is  still 
very  poor,  but  it  is  to  be  hoped  that  much  more  will  be 
learned  about  them  in  the  near  future  and  more  light 
shed  on  the  etiology  (science  of  cause  of  disease)  of  the 
diseases  which  are  the  result  of  "metabolic  disturb- 
ances." 

When  starch  has  been  digested;  that  is,  has  been  re- 
duced by  the  action  of  ptyalin,  amylase,  and  maltase  to 
the  absorbable  dextrose,  it  enters  the  capillaries  of  the 
intestinal  villi  and  is  carried  in  the  portal  circulation 
to  the  liver.  Normally,  AVC  have  1  to  2  per  cent  of  dex- 
trose in  our  blood,  but  it  is  evident  that  after  a  meal 
containing  much  starch  or  sugar,  the  amount  in  the 
portal  vein  must  be  much  more  than  this.  Should  this 
sugar-laden  blood  escape  into  the  general  circulation 
and  eventually  pass  through  the  kidneys,  these  organs 
would  not  be  able  to  retain  the  sugar  in  the  blood,  and 
it  would  be  passed  out  in  the  urine,  giving  rise  to  a 
"  glycosuria. "  The  liver,  however,  has  the  power  of 
fixing  this  dextrose  in  a  form  in  which  it  may  be  stored ; 
changing  it  into  the  glycogen  or  animal  starch  which 
has  already  been  mentioned.  Therefore,  after  a  meal 
containing  carbohydrate,  this  compound  can  be  easily 


FOOD   AND   DIGESTION  67 

detected  in  increased  amounts  in  the  liver.  The  volun- 
tary muscles  also  possess  the  same  "glycogenic"  func- 
tion, and  glycogen  is  deposited  in  them  also.  If  exces- 
sive amounts  of  a  readily  absorbable  sugar  is  fed,  the 
amount  entering  the  portal  circulation  is  too  great  for 
the  liver  and  muscles  to  handle,  and  some  of  the  dex- 
trose appears  in  the  urine.  This  condition  is  known  as 
"alimentary  glycosuria"  to  distinguish  it  from  the 
forms  of  glycosuria  due  to  disease.  When  need  arises 
the  glycogen  is  reconverted  into  dextrose  and  is  used  to 
yield  energy  to  contracting  muscles  or  secreting  glands 
or  to  other  functioning  tissues.  This  energy-yielding 
process  is  strongly  suggestive  of  a  similar  yield  of  en- 
ergy when  fuel  containing  carbon  and  hydrogen  is 
burned  outside  the  body,  and  the  end  results  of  the 
combustion  of  carbohydrate  either  in  the  body  or  out- 
side are  the  same,  namely,  water  and  the  gas,  carbon 
dioxide.  Occasionally,  we  see  persons  whose  tissues 
can  not  utilize  the  dextrose  furnished  them,  and  here, 
as  in  the  alimentary  glycosuria,  the  amount  of  dextrose 
in  the  blood  increases  beyond  the  amount  that  the  kid- 
neys can  hold  back  and  sugar  appears  in  the  urine. 
This  condition  constitutes  "diabetes  mellitus."  The 
wasting  away  that  usually  accompanies  severe  cases 
illustrates  the  importance  of  the  carbohydrates  in  the 
diet. 

When  larger  amounts  of  carbohydrates  are  fed, 
amounts  larger  than  are  needed  for  the  energy  require- 
ments, much  of  it  may  be  converted  into  fat  and  stored. 
The  well-known  effects  of  excessive  candy  eating  are 
explainable  on  this  basis.  To  a  verj^  small  extent,  carbo- 
hydrate may  be  used  to  help  build  up  the  tissues  of  the 
body,  but  this  occurs  in  such  a  limited  way  as  to  be 
negligible. 


68  PHYSIOLOGY  FOR   NURSES 

Under  the  influence  of  lipase,  fats  are  broken  up  into 
glycerin  and  free  fatty  acid.  Alkaline  salts  of  sodium, 
potassium,  magnesium,  and  calcium  are  present  in  the 
small  intestine,  and  these  bases  unite  with  the  fatty 
acids  to  form  soaps.  The  ordinary  toilet  soap  is  a 
similar  union  of  sodium  with  fatty  acid.  The  soaps  of 
sodium  and  potassium,  certainly,  pass  into  the  small 
lymph  channels  of  the  intestinal  villi,  being  reconverted, 
in  passing  through  the  absorbing  cells,  back  into  neu- 
tral fat;  i.e.,  the  union  of  glycerin  and  fatty  acid.  This 
food  fat  passes  on  in  the  lymph  channels  until  it  finally 
gains  entrance  to  the  veins  by  means  of  the  thoracic 
duct  and  the  right  lymphatic  duct,  and  by  this  means 
it  is  distributed  to  the  various  parts  of  the  body.  Fat, 
like  carbohydrate,  is  an  important  source  of  energy.  In 
the  body,  it  is  finally  reduced  to  the  same  forms  that 
carbohydrate  is,  carbon  dioxide  and  water,  being  ex- 
creted by  the  lungs  and  kidneys.  A  considerable 
amount  of  the  fat,  if  fed  in  excess,  may  be  deposited  in 
the  tissues,  to  serve  as  a  reserve  for  possible  subsequent 
need.  The  amount  of  fat  that  is  used  for  constructive 
purposes  may  be  disregarded. 

Under  certain  circumstances,  there  may  be  a  disturb- 
ance in  the  process  of  changing  the  fats  to  carbon  diox- 
ide and  water.  Inj  such  cases,  incompletely  oxidized 
substances  accumulate  in  the  blood ;  the  so-called  ' '  ace- 
tone bodies,"  acetone,  diacetic,  and  /^-oxybutric  acid. 
This  condition  is  known  as  "acidosis,"  and  may  arise  in 
the  course  of  diabetes  mellitus  or  even  in  simple  starva- 
tion. The  sodium  carbonate  of  the  blood  plays  an  im- 
portant part  in  carrying  carbon  dioxide  from  the  tissues 
to  be  excreted  by  the  lungs,  but  these  acetone  bodies 
require  a  considerable  amount  of  alkali  to  neutralize 
them,  so  that  the  normal  sodium  carbonate  content  of 


FOOD   AND   DIGESTION  69 

the  blood  is  reduced  and  carbon  dioxide  is  not  carried 
away  promptly.  This  explains  the  cyanosis  and  the 
labored  breathing. 

As  has  been  stated,  protein  may  be  broken  up  in  the 
body  to  yield  energy,  but  this  is  extravagant  for  two 
reasons;  first,  because  protein  food  is  actually  much 
more  expensive  and,  second,  that  it  probably  causes  more 
wear  and  tear  than  carbohydrate  on  the  body  when  used 
in  excessive  amounts.  The  most  important  role  of  protein 
is  to  serve  as  tissue-building  material,  a  role  for  which 
it  is  indispensable,  carbohydrate  and  fat  being  unable 
to  replace  protein  for  this  purpose. 

Under  normal  conditions,  all,  or  nearly  all,  of  the 
protein  is  absorbed  in  the  form  of  what  is  known  as 
"ammo  acids."  These  are  organic  acids  containing  the 
NH  or  amid  group,  and  are  known  as  the  "building 
stones"  of  the  proteins.  Under  the  combined  action  of 
pepsin,  trypsin,  and  erepsin,  this  decomposition  takes 
place,  and  the  amino  acids  enter  the  blood  vessels  of 
the  intestinal  villi  and  are  carried  to  the  liver  in  the 
portal  vein.  It  is  probable  that  the  liver  does  not  effect 
any  change  in  them  at  this  time,  but  allows  them  to 
pass  through  the  tissues  where  they  may  be  utilized. 
Wherever  there  is  need  of  building  material,  the  "build- 
ing stones"  are  taken  from  the  blood  and  utilized  to 
construct  the  particular  kind  of  protoplasm  needed. 

Even  with  the  ordinary  amounts  of  protein  in  the 
diet,  only  a  part  is  used  for  tissue  building  or  repair;  a 
considerable  portion  being  burned  to  yield  energy.  The 
end  products  of  this  breaking  up  of  protein  are  not  so 
simple  as  are  those  representing  the  final  results  of  car- 
bohydrate and  fat  decomposition.  Under  the  action  of 
tissue  enzymes,  the  nitrogen  is  split  off  and  is  carried  to 
the  liver.  Here  it  is  converted  into  "urea,"  which 


70  PHYSIOLOGY   FOR   NURSES 

passes  in.  the  blood  to  the  kidneys  and  is  excreted  in 
the  urine,  constituting;  the  chief  organic  substance  in 
the  urine  under  normal  conditions.  Tissues  which  wear 
out  and  are  broken  down  likewise  give  rise  to  the  pro- 
duction of  urea,  since  they  are  protein  material. 

Though  under  normal  conditions,  proteins  are  broken 
down  into  amino  acids  before  absorption,  nevertheless 
the  tissues  possess  the  power  to  break  down  more  com- 
plex protein  bodies  that  may  enter  the  circulation.  The 
occurrence  of  anaphylaxis  (literally  "without  a  guard") 
or  anaphylactic  shock  is  explained  in  this  way.  A  com- 
plex protein  body  is  introduced  into  the  circulation, 
either  by  subcutaneous  or  intravenous  injection  or  by 
passing  through  an  abnormal  mucous  membrane.  Hav- 
ing entered  the  circulation,  the  tissue  cells  elaborate  an 
enzyme  capable  of  decomposing  it  into  its  constituent 
"building  stones."  It  is  assumed  that  this  process  is 
rather  slow  and  gradual;  the  enzyme  is  produced  in 
small  amounts  so  that  there  is  no  poisoning  as  a  result 
of  the  first  introduction  of  the  foreign  protein.  Once 
the  enzyme  is  produced  by  the  tissue  cells,  however,  it 
remains  active  for  some  time.  Now,  at  some  later  time, 
if  the  same  protein  is  introduced  into  the  circulation, 
its  decomposition  starts  rapidly,  since  there  is  still  the 
necessary  enzyme  present.  As  a  result  of  this  rapid 
action,  intermediate  products  of  the  decomposition  are 
produced  in  large  enough  numbers  to  produce  mild, 
severe,  or  even  fatal  poisoning.  The  urticaria  (nettle 
rash)  often  seen  after  injection  of  diphtheria  antitoxin, 
asthmatic  attacks,  and  similar  manifestations  are  now 
considered  to  be  instances  of  anaphylaxis. 

It  has  already  been  pointed  out  that  carbohydrate, 
fat,  and  protein  are  required  for  proper  nutrition.  Pro- 
tein is  absolutely  essential  for  constructive  processes ; 


FOOD    AND   DIGESTION  71 

any  of  the  three  may  yield  energy,  but  on  an  exclusive 
protein  diet,  serious  disturbances  soon  arise.  There- 
fore, we  may  regard  protein  as  the  material  from  which 
new  tissue  is  built  or  by  which  old,  worn-out  tissue  is  to 
be  replaced,  while  fats,  and  especially  carbohydrates, 
are  the  fuel  foods;  all  three  being  needed  in  order  that 
growth  may  occur  or  that  health  may  be  preserved. 

It  becomes  a  matter  of  much  practical  importance  as 
to  how  much  of  each  constituent  should  be  included  in 
the  diet  and  what  the  total  should  be.  Fortunately, 
most  individuals  in  health  instinctively  select  the  proper 
amounts  needed  for  nutrition,  but  where  it  is  necessary 
for  the  physician  to  select  a  diet,  the  importance  of  this 
knowledge  is  obvious. 

It  has  been  learned  that  when  a  substance  is  burned, 
it  gives  off  a  definite  amount  of  heat,  and  by  suitable 
means,  this  heat  can  be  measured.  The  amount  of  heat 
required  to  raise  one  gram  of  water  one  degree  centi- 
grade is  known  as  the  small  calorie,  and  is  designated  by 
the  symbol  "cj"  the  amount  to  raise  the  temperature 
of  a  kilogram  of  water  a  similar  amount  is  known  as 
the  large  calorie,  and  its  symbol  is  "C."  If  one  gram  of 
carbohydrate  is  burned  under  suitable  conditions,  it  is 
found  that  it  yields  approximately  4.1  large  calories ; 
while  a  gram  of  fat  under  similar  conditions  yields  over 
twice  as  much  heat,  namely,  9.3  large  calories.  More- 
over, the  amount  of  heat  produced  in  the  animal  body 
by  the  oxidation  of  foods  can  be  measured,  and  it  is 
found  that  this  is  the  same  for  carbohydrate  and  fat  as 
that  produced  by  burning  these  substances  outside  the 
body.  In  the  oxidation  of  protein  in  the  body,  it  has 
been  found  that  a  gram  also  yields  about  4.1  large 
calories,  though  the  combustion  of  this  amount  of  pro- 
tein outside  the  body  gives  off  more  heat.  This  is  due 


72  PHYSIOLOGY  FOR   NURSES 

to  the  fact  that  protein  is  not  completely  burned  in  the 
body  but  some  of  the  end  results  of  its  metabolism  are 
still  capable  of  further  oxidation. 

By  studying  the  diets  of  large  numbers  of  individuals 
engaged  in  different  vocations,  it  has  been  learned  what 
the  average  amount  of  each  constituent  in  the  diet  is 
and  what  the  total  caloric  value  of  the  food  taken  in  24 
hours  should  be.  The  following  are  samples  of  average 
dietaries : 

TOTAL 
INVESTIGATOR       CARBOHYDRATE     FAT      PROTEIN     CALORIES 

Moleschott.  550  gm.  40  gm.         130  gm.  2980 

Ranke.  240  "  100  "  100  "  2324 

Voit.  500  "  56  «  118  "  3053 

It  is  seen  from  these  figures  that  the  amount  of  pro- 
tein is  not  subject  to  wide  variations,  while  reduction 
in  the  amount  of  carbohydrate  in  some  of  the  diets  is 
accompanied  by  increase  in  the  amount  of  fat  and  vice 
versa.  These  energy-yielding  foods  are  to  a  certain 
extent  mutually  replaceable,  but  there  is  a  limit  to  this : 
fat  being  more  difficult  of  digestion  and  also  more  ex- 
pensive. On  the  other  hand,  when  fat  is  not  absorbed 
properly  or  not  handled  properly  after  absorption,  even 
though  there  be  no  evidence  of  disturbance  with  the 
metabolism  of  protein  and  carbohydrates,  severe  nutri- 
tional disturbances  occur,  as  illustrated  by  cases  of 
injury  to  the  thoracic  duct  or  of  faulty  fat  digestion,  the 
latter  occurring  in  infancy. 

Agreement  has  not  yet  been  reached  in  regard  to  the 
amount  of  protein  required  in  the  diet.  As  shoAvn  above, 
in  no  instance  is  it  below  100  grams  in  24  hours  in  the 
average  diet.  This  amount  is  in  excess  of  what  is  re- 
quired for  repair  of  tissue  in  the  adult  under  normal 
conditions,  a  considerable  part  of  the  ingested  protein 
being  split  up  to  yield  energy.  Since  protein  is  more 


FOOD    AND   DIGESTION  73 

expensive,  both  in  actual  cost  and,  possibly,  on  account  of 
its  influence  on  the  cells  of  the  animal  using  it,  the  ques- 
tion has  arisen  whether  we  could  not  advantageously  re- 
duce the  amount  in  our  diets.  It  has,  indeed,  been  shown 
that  for  considerable  periods  of  time  the  amount  may  be 
reduced  to  less  than  a  half  of  the  amount  given  in  the 
dietaries  above  with  no  apparent  impairment  of  the  per- 
son's health  or  efficiency.  Against  this,  however,  is  the 
fact  that,  left  to  himself,  normal  man  takes  the  larger 
amount  of  protein  in  his  diet,  regardless  of  his  condition 
or  occupation.  When  one  is  engaged  in  work  necessitating 
much  muscular  exertion,  a  greater  number  of  calories  is 
required,  but  when  this  is  the  case,  the  increase  is  made 
largely  with  the  carbohydrate  and  fat,  the  laborer  using 
actually  little  more  protein  than  the  clerk  who  leads  a 
sedentary  life. 

Since  urea,  resulting  from  protein  decomposition  in 
the  body,  is  excreted  by  the  kidneys,  it  has  been  sug- 
gested that  large  amounts  of  protein  in  the  diet  will 
throw  extra  work  on  these  organs  and  tend  to  injure 
them.  Then,  too,  it  has  been  pointed  out  that  the  putre- 
faction of  proteins  that  may  take  place  in  the  intestines, 
gives  rise  to  poisonous  substances,  which  entering  tiie 
circulation,  may  damage  both  liver  and  kidneys.  These 
are  theoretical  conditions,  however,  which  are  still  far 
from  proved. 

Tn  some  recent  work,  it  has  been  pointed  out  that  not 
all  proteins  are  li adequate"  for  nutrition.  It  is  essen- 
tial that  certain  of  the  "building  stones"  be  present, 
and  if  the  protein  is  deficient  in  these  it  does  not  suffice 
for  the  purposes  of  maintenance  or  for  the  promotion  of 
growth.  Gelatin  is  an  illustration  of  one  of  the  inade- 
quate proteins.  It  was  formerly  believed  that  gelatin 
was  capable  of  supplying  the  protein  in  the  diet,  and 


74  PHYSIOLOGY   FOR   NURSES 

the  experiment  was  tried  011  a  large  scale  in  France, 
but  this  experiment  was  a  failure,  for  the  reason  already 
given. 

The  mineral  salts  are  absolutely  indispensable  in  the 
diet,  and  it  is  stated  that  death  will  occur  in  an  animal 
fed  on  an  abundance  of  salt-free  food  sooner  than  with 
one  deprived  entirely  of  all  food.  This  is  because  the 
organic  food  leads  to  the  excretion  of  the  salts  in  the 
tissues. 

Sodium  chloride,  or  ordinary  salt,  is  the  only  one  of 
the  salts  that  we  consciously  add  to  our  diet.  When  the 
diet  consists  of  a  considerable  amount  of  vegetable  food, 
the  need  of  sodium  chloride  becomes  more  apparent,  and 
herbivorous  animals  show  the  same  desire  for  salt  that 
human  beings  do. 

The  sodium  chloride  plays  a  very  important  role  in 
our  bodies.  It  is  the  chief  inorganic  constituent  of  our 
blood  plasma  and  it  is  essential  for  the  production  of 
hydrochloric  acid  of  the  gastric  juice.  It  is  also  sup- 
posed to  exert  an  influence  on  the  contractions  of  the 
heart.  The  urine  contains  a  considerable  amount  of 
this  salt,  and  in  certain  cases  of  diseased  kidneys,  diffi- 
culty is  experienced  by  these  organs  in  eliminating  the 
sodium  chloride.  As  a  result  of  this,  there  occurs  a 
salt  retention  and  the  salt  also  retains  fluid,  giving  rise 
to  the  accumulation  of  fluid  in  the  tissues,  known  as 
edema  or  dropsy. 

Salts  of  calcium  are  also  important.  They  influence 
the  contraction  of  the  heart  and  also  the  irritability  of 
muscle  and  nerve.  Calcium  is  found  in  large  amounts  in 
the  bones,  and  clotting  of  blood  and  curdling  of  milK 
can  not  take  place  in  the  absence  of  calcium.  Potassium 
salts  influence  the  heart,  while  the  salts  of  iron  are  of 


FOOD   AND   DIGESTION  75 

importance  in  constituting  an  essential  part  of  hemo- 
globin, the  oxygen-carrying  pigment  of  the  blood. 

Even  if  the  diet  contains  sufficient  amounts  of  carbo- 
hydrate, fat,  and  protein,  with  an  adequate  supply  of 
mineral  salts  and  water,  it  is  found  that  nutritional 
disturbances  will  occur  eventually,  unless  certain  or- 
ganic substances  in  addition  be  included.  These  sub- 
stances may  be  nitrogenous  in  nature  or  may  be  free 
from  nitrogen.  They  are  not  energy-yielding  foods, 
nor  are  they  used  for  constructive  purposes;  but,  ap- 
parently, they  exert  a  very  marked  influence  on  the 
processes  of  metabolism.  They  are  known  as  "vita- 
mines  "  or  as  "  growth-promoting  factors. ' '  The  first  one 
to  be  studied  is  that  occurring  in  the  pericarp  (the  part 
which  surrounds  the  kernel)  of  rice,  the  absence  of 
which  gives  rise  to  the  peculiar  disease  known  as  "beri- 
beri." Scurvy,  also,  was  formerly  held  to  be  a  disease 
due  to  the  absence  of  vitamines  from  the  diet,  though 
this  has  been  denied  recently.  Certain  fats  contain  the 
requisite  "growth-promoting"  factors,  while  others  do 
not;  butter  and  cod-liver  oil  being  instances  of  the 
former,  while  lard  is  an  example  of  the  latter  class. 


CHAPTER  IV 

THE  FUNCTIONS  OF  THE  LIVER 

That  the  liver  plays  an  important  part  in  the  nutri- 
tion of  the  body  might  be  inferred  both  from  the  size 
of  the  organ  and  the  enormous  stream  of  blood  poured 
into  it  by  the  portal  vein;  for  in  addition  to  the  hepatic 
artery,  which  carries  blood  to  nourish  the  tissue  of  the 
organ,  the  portal  vein,  which  receives  blood  from  the 
entire  digestive  and  absorptive  tract, '  pours  this  great 
stream  of  blood  into  the  doorway  of  the  liver,  plainly 
not  for  the  benefit  of  that  organ,  but  that  it  may  effect 
necessary  changes  in  tiie  material  of  which  this  blood 
alone  is  the  bearer.  Three  such  changes  appear;  i.e., 
the  secretion  of  bile  and  the  formation  of  glycogen  and 
urea. 

Bile  is  partly  an  excretion  of  substances  to  be  re- 
moved and  partly  a  secretion  of  a  product  useful  but 
not  essential  to  digestion.  Ii  is  secreted  at  all  times  but, 
in  man,  is  stored  in  the  gall  bladder  and  ejected  into 
the  duodenum  only  when  needed.  The  quantity  formed 
in  a  day  is  from  500  to  800  c.c.  The  color,  in  man,  is  a 
greenish  yellow.  It  contains  about  97l/2  per  cent  water 
and  about  21/2  per  cent  solids  of  which  the  chief  are 
bile  pigment,  derived  from  broken-down  red  blood  cor- 
puscles, bile  acids,  taurocholate,  and  glycocholate  of 
soda,- — fats,  soaps,  lecithin,  a  substance  which  occurs  in 
greatest  quantity  in  the  white  matter  of  the  nervous 
system,  and  cholestcrin. 

Bile  pigment  is  called  ~bilirubin  when  red,  and  bili- 
verdin  when  green.  The  pigments  appear  to  be  re- 

73 


FUNCTIONS    OF    THE   LIVER 


77 


absorbed  from  the  intestines  into  the  portal  circulation 
and  carried  to  the  liver  which  again  extracts  them  from 
the  blood.  This  is  called  the  circulation  of  the  bile. 

Secretion  of  Bile. — It  is  believed  that  there  are  no 
special  secretory  nerve  fibers  whose  stimulation  excites 
the  secretion  of  bile.  Apparently  the  flow  is  automati- 
cally regulated  by  the  blood  flow,  since  stimulation  of 
the  splancJiic  nerves,  which  carry  vasomotor  fibers  to 
the  liver,  increases  the  flow  of  bile.  Secretin,  whose 


Fig.  16. — The  microscopic  structure  of  the  liver.  (Highly  magnified.) 
A,  Lobule,  showing  the  intralobular  plexus;  B,  Lobule  showing  the  hepatic 
cells.  (Buchanan's  Anatomy.) 

action  on  pancreatic  secretion  has  been  related,  stimu- 
lates the  flow  of  bile.  As  soon  as  the  acid  chyme  is 
thrown  into  the  duodenum,  not  only  is  the  activity  of 
the  liver  excited,  but  the  gall  bladder  is  stimulated  to 
contract  and  there  is  an  outflow  of  ready  formed  bile 
into  the  duodenum.  When  this  is  prevented,  as  by  a 
gallstone  plugging  the  bile  duct,  or  from  any  cause,  bile 
gets  into  the  blood  and  the  condition  of  jaundice  is 
produced. 


78  PHYSIOLOGY   FOE   NURSES 

Function  of  Bile. — Whatever  its  other  effects,  the 
chief  known  use  of  bile  is  in  promoting  the  digestion 
and  absorption  of  fats.  It,  in  some  way,  prevents  putre- 
faction in  the  intestines,  though  this  is  not  the  result  of 
germicidal  action,  which  bile  does  not  possess. 


i  ,>«.  ;w 


b.d. 


Fig.   17. — Portion  of  transverse  section  of  human  liver.     X.  100.     h.a.,  hepatic 
artery;  v.c.,  intralobular  vein;  v.p.,  interlobular  vein;  b.d.,  bile  duct. 


FUNCTIONS    OF    THE   LIVER  79 

Glycogenic  Function  of  the  Liver. — Glycogen,  or  ani- 
mal starcli  can  be  detected  by  the  microscope  in  the 
cells  of  the  liver,  increasing  after  meals  and  decreasing 
during  the  hours  of  fasting,  and  varying  with  the  kind 
and  quantity  of  food,  exercise,  etc.  The  amount  in  the 
liver  varies  between  1.5  and  4  per  cent  of  the  weight  of 
the  liver.  Glycogen  is  chiefly  derived  from  starchy 
foods,  though  proteins  may  furnish  small  amounts.  Fats 
seem  to  increase  the  amount  of  glycogeii  in  the  liver  by 
preventing  its  consumption  in  other  parts  of  the  body. 

GLYCOGEN  THEORY. — The  theory  of  this  function  of  the 
liver  is  that  it  maintains  the  sugar  equilibrium  of  the 
body;  that  is,  that  an  increase  of  carbohydrate  food 
would  always  be  followed  by  an  increase  of  sugar  in 
the  blood  if  the  liver  did  not  convert  the  dextrose  and 
other  sugars  into  animal  starch  which  it  stores  up  until 
a  fasting  period,  or  at  least  decrease  of  the  normal 
sugar  content  of  the  blood,  calls  for  a  renewal  of  the 
supply,  when  the  stored  glycogen  of  the  liver  is  recon- 
verted into  sugar  and  given  up  to  supply  the  deficiency. 
This  conversion  appears  to  be  accomplished  by  a  special 
enzyme  formed  for  the  purpose,  in  the  liver. 

The  liver  is  not  the  only  store  house  for  glycogen. 
It  is  estimated  that  the  red  muscles  of  the  body  contain 
as  much  of  this  starch  as  the  liver  itself,  and  that  it  is 
used  up  more  rapidly  when  the  muscle  is  active  than 
when  passive. 

Urea-Forming  Function  of  the  Liver. — Urea  is  the 
chief  form  in  which  nitrogen  is  removed  from  the  body. 
This  product  of  protein  food  is  eliminated  from  the 
blood  by  the  kidneys,  but  it  is  formed  in  the  liver  and 
sent  to  the  kidneys  only  to  be  extracted.  No  doubt  the 
liver  is  not  the  only  source  of  urea,  but  it  is  at  least 
a  demonstrated  source  of  this  end  product  of  protein 
digestion. 


CHAPTER  V 

THE  SPLEEN 

A  chapter  on  the  physiology  of  the  spleen  may  be  al- 
most as  brief  as  the  history  of  snakes  in  Ireland,  for  al- 


Y^0"1 


Fig.  18. — Vertical  section  of  human  spleen  (modified  from  Kolliker),  low 
power,  t,  trabeculae;  m,  Malpighian  corpuscles;  b,\  injected  arterial  twigs; 
s.p.,  spleen  pulp.  The  clear  spaces  are  the  venous  sinuses. 

most  nothing  is  positively  known  of  the  function  of  the 
organ.  It  not  only  has,  in  proportion  to  its  size,  a  very 
abundant  blood  supply,  but  its  return  circulation  is  car- 

80 


THE    SPLEEN  81 

ried  into  the  portal  vein  and  thence  through  the  liver, 
indicating  that  it  effects  some  changes  in  the  blood 
which  the  liver  must  perfect;  yet  its  removal  neither 
causes  the  death  of  the  animal  nor  effects  any  perma- 
nent changes  in  the  character  of  the  blood. 

That  it  is  associated  with  digestive  processes  is  shown 
by  the  fact  that  it  slowly  increases  in  size  after  a  meal 
for  about  five  hours  and  then  returns  to  its  normal  size. 

Its  activity  is  supposed  to  be  directed  to 

I.  The  formation  of  new  red  blood  corpuscles,  a  work 
which  it  certainly  does  during  fetal  life. 

II.  The  destruction  of  old  and  damaged  red  blood  cor- 
puscles, a  supposition  founded  largely  on  the  spleen's 
richness  in  iron. 

III.  The  production  of  uric  acid,  an  inference  from 
the  presence  of  other  bodies  from  which  uric  acid  can  be 
the  presence  of  other  bodies  from  which  uric  acid  can  be 
formed. 


CHAPTER  VI 
FUNCTIONS  OF  THE  KIDNEY 

All  the  waste  matter  of  digestion  and  of  bodily  activ- 
ity is  not  carried  away  in  the  feces.  Some  elimination, 
particularly  of  water,  takes  place  through  the  lungs, 
some  through  the  skin,  but  the  major  part  through  the 
kidneys.  The  product  of  the  activity  of  this  pair  of  or- 
gans is  the  urine. 

Urine,  in  man,  is  a  more  or  less  straw-colored  fluid,  the 
color  varying  greatly  even  in  health  and  still  more  in 
disease,  from  an  almost  colorless  liquid  to  a  dusky  red. 
Urine,  in  health,  shows  a  slightly  acid  reaction,  i.e., 
turns  blue  litmus  paper  red,  due  to  the  presence  of  salts, 
chiefly  sodium,  so  combined  as  to  form  acid  phosphates. 
This  activity  is  increased  on  an  animal  diet  and  dimin- 
ished on  a  vegetable  diet,  sometimes  even  disappearing 
so  that  the  urine  is  neutral, — has  no  action  on  litmus  pa- 
per or  even  turns  red  litmus  blue;  the  urine  becomes 
alkaline  in  reaction.  The  average  specific  gravity  of 
urine  is  1.020.  The  amount  passed  in  a  day  is  from  two  to 
three  pints  but  varies  under  so  many  conditions,  even 
in  health,  that  a  specific  amount  can  not  be  stated.  In 
general  the  statement  may  be  made  that  the  amount  of 
urine  varies  more  from  the  activity  of  the  skin  than 
from  any  other  single  condition.  Thus,  in  warm 
weather,  when  one  perspires  freely,  the  amount  of  urine 
will  decrease  and  the  color  will  be  high.  Exercise,  or 
any  other  condition,  which  increases  the  formation  of 
sweat,  will  decrease  the  amount  of  urine.  A  cold  bath 
or  a  sudden  change  of  weather  to  a  lower  temperature, 

82 


FUNCTIONS   OF   THE   KIDNEY  83 

increases  the  urinary  secretion.  Children  discharge 
more  urine  than  adults,  and  women,  relatively  more 
than  men.  Even  mental  conditions  affect  the  flow,  as  is 
evidenced  in  hysteria  when  loss  of  nervous  control  enor- 
mously increases  the  output.  Diet  largely  affects  both 
the  quantity  and  the  contents;  and,  of  course,  the 
amount  of  liquid  taken  will  act  even  more  decidedly  and 
more  rapidly.  Drinking  a  quantity  of  water  will  increase 
the  flow ;  but  drinking  the  same  amount  of  beer  will  not 
only  cause  a  greater  flow,  but  the  increase  will  occur 
earlier.  Many  drugs,  called  diuretics,  produce  the  same 
effect,  while  others  will  diminish  the  quantity. 

Composition  of  Urine. — Urine  holds  a  large  number 
of  different  bodies  in  solution,  but  is  chiefly  notable  be- 
cause it  takes  away  the  product  of  the  digestion  of  ni- 
trogenous food  in  the  form  mainly  of  urea. 

Urea  is  the  most  important  nitrogenous  element  in 
the  urine.  That  urea,  or  some  antecedent  substance,  is 
formed  largely  in  the  liver  seems  certain.  It  is  present 
in  the  blood  and  other  tissues  and  so  large  a  part  of  the 
total  output  is  removed  by  the  kidneys  that  the  removal 
of  both  of  these  organs  ahvays  causes  death.  The  aver- 
age amount  excreted  in  twenty-four  hours  is  from  350 
to  450  grams.  Drinking  large  quantities  of  water  will 
decrease  the  relative  but  increase  the  actual  amount  of 
urea,  while  an  increase  in  nitrogenous  food  increases, 
and  of  vegetable  food,  diminishes,  the  output  of  urea. 
Exercise,  or  anything  which  increases  metabolism  of  tis- 
sue, increases  the  amount  of  urea. 

Uric  acid  as  such  does  not  occur  in  urine  in  health, 
but  in  the  form  of  urates,  chiefly  of  sodium  though  sim- 
ilar salts  of  potash,  lime,  magnesia  and  ammonia  are 
found.  From  ten  to  fifteen  grains  of  urates  are  ex- 
creted daily.  They  are  not  formed  in  the  kidneys,  but 


84  PHYSIOLOGY   FOR   NURSES 

exist  in  the  blood  and  are  merely  extracted  from  it  by 
those  organs.  They  increase  greatly  in  gout. 

Creatinin,  xanthin,  hypoxanthin  are  other  nitroge- 
nous bodies  which  exist  in  small  quantities  in  the  urine. 

Hippuric  acid,  in  the  form  of  hippurates,  has  the  pe- 
culiarity of  being  a  body  formed  by  the  kidneys  and  not 
preexisting  in  the  blood.  It  is  increased  by  a  vegetable 
diet. 

Of  the  nonnitrogenous  bodies  occurring  in  normal 
urine,  sodium  chloride,  common  table  salt,  is  the  most 
abundant.  About  151  grains  are  eliminated  daily.  Some 
mucus  derived  from  the  bladder,  is  a  constituent  of 
normal  urine. 

Urochrome,  said  to  be  formed  from  hemoglobin,  is  the 
coloring  matter  of  the  urine. 

Any  of  the  bodies  mentioned  above,  may  be  increasod 
or  decreased  in  diseased  conditions  and  others  may  be 
present,  from  disease  or  injury,  which  do  not  exist  in 
normal  urine.  The  examination  of  the  urine  in  health 
and  disease  is,  therefore,  a  routine  matter  for  the  doc- 
tor and  one  with  which  the  nurse  should  be  familiar. 

Some  of  the  chief  abnormal  constituents  are  blood, 
pus  or  cells  derived  from  any  part  of  the  urinary  tract 
— kidneys,  ureters,  bladder  or  urethra;  albumin,  wnich 
coagulates  when  urine  is  heated;  sugar,  in  the  form  of 
fjrapc  sugar  most  frequently;  casts  from  the  tubules  of 
the  kidney;  free  uric  acid;  stones  formed  of  salts  nor- 
mally found  in  the  urine  and  many  others  too  numerous 
to  mention.  The  tests  for  these  substances  will  be  found 
in  works  on  urinary  analysis. 

Urinary  Organs. — The  urinary  organs  are  the  kidneys, 
which  extract  urine  from  the  blood;  the  ureters,  ducts 
of  the  kidneys,  one  for  each,  which  convey  urine  to  the 
bladder  or  reservoir  which  retains  the  fluid  until  its  dis- 


FUNCTIONS    OF    THE    KIDNEY 


85 


tention  calls  for  relief,  and  the  uretlira,  or  tube,  or  duct, 
of  the  bladder  through  which  the  urine  is  voided. 

The  kidney  is  a  compound  tubular  gland  which,  when 
split  from  outer  to  inner  border,  is  seen  to  consist  of  an 
outer  or  cortical  portion;  an  inner  pyramidal  or  medul- 
lary portion  and  a  deep  concavity,  the  Jiilum,  filled  by 


Fig.  19. — Longitudinal  section  through  the  kidney:  /,  Cortex;  i' ,  med- 
ullary rays;  i" ,  labyrinth;  2.  medulla;  2',  papillary  portion  of  medulla; 
2",  boundary  layer  of  medulla;  3,  transverse  section  of  tubules  in  the 
boundary  layer;  4,  fat  of  renal  sinus;  5,  artery;  *,  transverse  medullary 
rays;  A,  branch  of  renal  artery;  C,  renal  calyx;  U,  ureter  (after  Tyson  and 
Henle). 


blood  vessels  and  the  pelvis  or  beginning  of  the  ureter. 
The  cortical  area,  about  two-thirds  of  the  organ,  is  the 
active,  secretory  portion  of  the  kidney,  the  remainder 
being  the  collecting  area.  In  the  cortical  portion  are 
found  the  glomeruli  and  convoluted  tubules  which  re- 
move the  urine  from  the  blood,  while  in  the  medullary 


86 


PHYSIOLOGY   FOR   NURSES 


s  ID 


op 


Fig.  20. — Diagrammatic  representation  of  the  course  of  the  uriniferous  tubules 
and  the  kidney  vessels. 


FUNCTIONS   OF   THE   KIDNEY  87 

substance  are  seen  the  pyramids  of  Malpighi,  whose 
apices  open  into  the  caUces  or  first  branches  of  the  ure- 
ter. Histology  must  be  consulted  for  the  minute  anat- 
omy of  the  organ. 

As  no  distinct  secretory  nerve  fibers  have  been  demon- 
strated in  the  kidney,  the  mechanism  of  the  secretion  of 
urine  can  be  explained  only  by  supposing  that  a  part  of 
the  process  is  simple  filtration  or  osmosis,  depending  on 
an  abundant  blood  supply  with  sufficient  pressure,  while 
the  remainder  is  due  to  the  " vital  action"  of  the  cells 
lining  the  glomeruli  and  tubules.  "Assuming  that 
nearly  all  the  constituents  of  urine  preexist  in  the  blood 
and  are  simply  taken  out  of  the  circulation  by  the  kid- 
ney, it  may  be  stated  that,  for  the  most  part,  the  water 
and  salts  are  extracted  by  the  cells  of  the  Malpighian 
bodies,  while  the  urea  and  related  nitrogenous  solids  are 
removed  by  the  cells  of  the  convoluted  tubes ;  so  that  the 
specific  gravity  of  the  fluid  is  raised  by  passing  down 
the  tubes."  (Jones  and  Bunce).  Diuretics  may  act, 
therefore,  by  increasing  the  amount  of  blood  flowing 
through  the  kidney,  by  increasing  the  pressure  of  the 
blood,  by  promoting  osmosis  or  by  stimulating  cell  ac- 
tivity. 

After  urine  has  been  formed  in  the  kidney  it  is  col- 
lected in  the  pelvis  of  the  ureter,  which  contracts  to  the 
ureter  proper,  a  long  slender  tube  partly  composed  of 
nonstriated  muscle  fiber,  which  runs  behind  the  perito- 
neum to  the  bladder,  and  enters  the  bladder  so  obliquely 
that  the  weight  of  urine  in  that  organ  presses  on  and 
closes  the  ureteral  openings  and  prevents  any  back  flow 
of  urine.  It  is  well  to  remember  that,  in  the  female  the 
neck  of  the  uterus  is  between  the  two  ureters  just  be- 
fore they  enter  the  bladder. 

The  bladder  is  an  ovoid  muscular  sac  which  receives 


88  PHYSIOLOGY  FOR   NURSES 

and  retains  the  urine  until  distended  moderately  when 
there  is  a  desire  to  urinate.  The  neck  of  the  bladder  is 
surrounded  by  a  thickening  of  plain  muscle  fiber  form- 
ing a  spliincter,  or  ring-like,  muscle,  whose  constant  con- 
traction prevents  the  dribbling  away  of  urine  as  fast  as 
it  enters  the  bladder. 

Micturition  is  the  act  of  emptying  the  bladder.  The 
urine  is  forced  along  the  ureters  by  contraction  of  the 
muscular  coats  of  those  tubes  every  ten  or  twenty  sec- 
onds so  that  it  enters  the  bladder  in  small  jets  and  not  as 
a  steady  flow.  When  the  bladder  is  being  filled,  the  pres- 
sure causes  a  stimulation  of  the  fibers  of  the  sphincter, 
through  the  sensory  nerves,  and  the  contraction  of  this 
muscle  prevents  the  escape  of  the  urine.  A  further  ac- 
cumulation of  urine  increases  the  pressure  on  the  sen- 
sory nerves  and,  by  a  reflex  act,  causes  a  contraction  of 
the  muscular  coats  of  the  bladder,  an  inhibition  of  the 
center  in  the  lumbar  part  of  the  spinal  cord  which  con- 
trols the  sphincter,  which  is  consequently  relaxed,  al- 
lowing the  urine  to  flow  freely  along  the  urethra. 

Fullness  of  the  bladder  is  not  the  only  stimulus  that 
causes  a  desire  to  urinate.  An  irritating  quality  in  the 
urine  itself,  which  may  be  caused  by  some  drugs,  men- 
tal conditions,  like  anxiety  or  other  emotion,  may  create 
a  desire  to  void  the  urine  when  the  bladder  is  not  only 
not  full,  but  when  nearly  empty.  This  seems  to  be  due 
to  changes  of  tone  in  the  bladder  muscle  itself. 

The  urethra  in  the  female  is  a  much  shorter  channel 
than  in  the  male.  As  the  catheter  is  an  instrument  very 
frequently  used  by  the  nurse,  she  should  be  familiar 
with  the  normal  urethra.  In  woman  the  canal  is  so  short 
and  wide  that  the  passage  of  the  catheter  is  usually  very 
easy.  In  man,  however,  the  contraction  of  the  muscular 
fibers  around  the  bulbous  part  of  the  urethra  frequently 


FUNCTIONS   OF    THE   KIDNEY  89 

offers  a  temporary  obstacle  which  is  overcome  by  gentle 
pressure.  The  elongated  urethra  of  old  prostatic  cases 
need  only  be  mentioned. 

Nerve  Control. — The  subject  of  nerve  control  is  not 
completely  understood.  That  there  is  a  center  control- 
ling micturition  in  the  lumbar  cord  and  that  sensory 
nerves  pass  from  the  bladder  to  the  cord  and  motor 
nerves  from  the  cord  to  the  bladder,  is  clear,  but  the  ex- 
act paths  are  not  so  well  known.  That  this  center,  like 
that  for  defecation,  is  under  the  control  of  the  will  in 
adult  life  is  a  matter  of  daily  observation ;  but  that  this 
control  is  acquired  is  plain  from  the  habits  of  infancy 
and  from  the  involuntary  passages  of  urine  and  feces  in 
the  unconsciousness  of  severe  illness,  is  equally  obvious. 


CHAPTER  VII 

THE  FUNCTIONS  OF  THE  SKIN 

The  importance  of  the  skin  is  made  apparent  when  one 
considers  that  the  destruction  of  a  third  of  that  cover- 
ing is  nearly  always  fatal.  Primarily  its  function  is  pro- 
tective, as  is  shown  by  its  position  between  the  easily  in- 
jured inner  tissues  and  the  outer  world.  It  contains  those 
nerve  terminals  which  give  the  inner  consciousness  warn- 
ing against  pain,  pressure,  heat  or  cold,  sharp,  rough  or 
otherwise  injurious  objects.  It  contains  the  sweat  glands 
which  aid  in  the  elimination  of  harmful  matter  and  as- 
sist in  regulating  the  body  temperature;  and,  in  the  fe- 
male, through  the  mammary  gland,  it  supplies  nourish- 
ment to  the  infant. 

Sweat,  or  Perspiration,  is  the  secretion  of  the  sweat 
glands  which  are  found  in  nearly  every  part  of  the  SKHI, 
though  most  abundant  in  the  palms  of  the  hands  and 
soles  of  the  feet.  The  number  for  the  entire  body  is  es- 
timated to  be  about  two  million.  They  are  simple  tubu- 
lar glands,  lined  by  columnar  epithelium,  usually  coiled 
and  having  a  thin  muscular  coat  surrounding  the  larger 
ducts.  The  average  quantity  of  sweat  in  twenty-four 
hours  is  from  700  to  900  grams,  though  the  amount  va- 
ries greatly  with  the  temperature  and  moisture  of  the  at- 
mosphere and  the  exertion  of  the  individual.  It  is  a 
thin  watery  fluid  with  a  low  specific  gravity  and  an  al- 
kaline reaction,  which  contains  chloride  of  soda,  urea, 
uric  acid  and  various  other  organic  bodies.  The  influ- 
ence of  profuse  sweating  on  the  amount  of  urine  has  al- 
ready been  stated.  To  a  limited  degree  the  skin,  through 

90 


FUNCTIONS   OF   THE   SKIN  91 

the  sweat  glands,  can  relieve  the  overburdened  kidneys, 
a  fact  which  is  taken  advantage  of  to  induce  sweating, 
by  drugs  or  other  means,  when  the  kidneys  do  not  prop- 
erly perform  their  function,  as  in  the  condition  of  ec- 
lampsia which  sometimes  endangers  a  woman  in  child- 
bearing. 

Nerve  Control. — There  is  reason  to  conclude  that  there 
is  a  sweat  center,  probably,  in  the  medulla  and  perhaps 
subsidiary  centers  in  the  cord.  Secretory  fibers  are  car- 
ried directly  to  the  glands  and  are  ordinarily  excited  by 
high  temperature,  which  acts  reflexly  through  the  cen- 
tral nervous  system.  Heat  alone  will  not  cause  sweat- 
ing. In  the  high  temperatures  of  fever,  sweating  is 
notably  absent,  while '  present  in  profuse  degree  in  the 
pale  skin  of  the  terror  stricken.  This  proves,  also,  that 
an  increase  in  the  amount  of  blood  in  the  skin  is  not 
enough  to  cause  sweat,  and  that  a  decrease  does  not 
prevent  its  secretion.  Many  drugs,  like  pilocarpin  will 
increase  the  activity  of  the  sweat  glands  and  some,  like 
atropin  will  paralyze  the  secretory  fibers. 

Sebaceous  Glands  .—These  simple  or  compound  alve- 
olar glands  are  usually  found  associated  with  the  hairs, 
when  their  ducts  open  directly  into  the  hair,  follicles. 
The  cells  which  line  them  are  cast  off  apparently  as  a 
part  of  the  secretion  of  the  glands,  sebum,  which  is  an 
oily  semiliquid  which  sets  into  a  cheesy  mass,  such  as 
can  be  squeezed  from  the  pimples  or  comedones,  which 
disfigure  many  people  when  the  ducts  become  stopped. 
The  secretion  of  those  glands  located  in  the  ear,  when 
mixed  with  that  of  other  glands,  forms  ear  wax.  The 
secretion  of  the  sebaceous  glands  probably  forms  an 
oily  coating  for  the  SKin  and  hairs  which  protects  the 
former  by  preventing  too  rapid  evaporation  and  keeps 
the  latter  from  becoming  too  dry  and  brittle. 


92  PHYSIOLOGY   TOR   NURSES 

Iii  addition  to  these  active  and  important  excretory 
functions  of  the  skin,  there  is  a  slight  power  of  remov- 
ing carbon  dioxide. 

Cutaneous  Sensations. — Everyone  is  aware  of  a  capac- 
ity to  feel;  i.e.,  a  sense  of  touch,  or  tactile  sense;  and  to 
distinguish  between  rough  and  smooth,  sharp  and  blunt, 
hot  and  cold,  heavy  and  light  objects,  etc.  These  are 
among  our  cutaneous  sensations,  though  the  last  two  are 
more  properly  muscle  sensations.  The  capacity  to  feel 
pain  is  more  widely  distributed  than  the  other  skin  sen- 
sations. 

Nerves  which  convey  information  to  the  brain  from 
any  portion  of  the  body  are  called  sensory,  or  afferent, 
and  each  nerve  ending  responds  to  but  one  stimulus;  i.e.. 
can  carry  information  of  but  one  kind.  Thus  if  the 
nerve  of  sight  is  cut,  no  pain  is  felt,  but  only  a  riash 
of  light  will  be  recognized  by  the  brain. 

Observation  has  proved  that  there  are  four  stimuli 
which  can  excite  the  nerves  distributed  to  the  skin, 
which  will  convey  four  kinds  of  information  to  the 
brain.  These  four  sensations  are  heat,  cold,  pressure  or 
touch  and  pain.  Careful  experiments  have  shown  that 
minute  areas  of  skin  are  sensitive  to  one  or  another  of 
these  stimuli  and  to  no  other.  Such  areas  are  designated 
lieat  spots,  cold  spots,  pressure  or  pain  spots.  If  one 
touches,  with  a  delicate  instrument,  a  cold  spot,  a  sen- 
sation of  cold  will  be  experienced,  even  if  the  instrument 
itself  is  u'unHf'r  Hum  the  skin..  Cold  spots  are  more  nu- 
merous than  warm;  pressure  points  more  numerous  than 
either  and  pain  spots  the  most  numerous  of  all.  Some 
portions  of  the  body  envelope,  like  the  membrane  cover- 
ing the  eyeball,  have  no  nerve  spots  except  those  of 
pain,  which  are  present  in  great  numbers.  Pressure 
spots,  supposed  to  number  about  half  a  million  for  the 


FUNCTIONS   OF   THE   SKIN  93 

entire  body,  are  found  in  rings  around  hair  follicles,  the 
hairs  acting  like  levers  can  thus  give  rise  to  the  sense 
of  pressure  or  touch  when  nothing  has  touched  the  skin, 
as  when  an  insect  crawls  over  the  hair  or  when  the  wind 
moves  it. 

Certain  areas,  like  the  tips  of  the  fingers,  and  the  tip 
of  the  tongue  are  very  abundantly  supplied  with  touch 
nerves,  while  other  parts,  like  the  middle  of  the  back, 
have  pressure  spots  only  at  comparatively  wide  inter- 
vals, and  it  would  seem  that  the  number  may  be  in- 
creased by  use,  as  is  seen  in  the  delicate  sense  of  touch 
possessed  by  the  blind,  or  in  the  fingers  of  a  trained  sur- 
geon. At  least  the  nerve  terminals  may  be  educated  and 
become  more  sensitive.  Skin  sensations  are  as  much  or- 
gans of  special  sense  as  the  eye  or  ear  and  capable  of 
as  much  improvement  by  training.  From  this  it  would 
appear  that  some  persons  not  only  cry  out  more  than 
others  under  the  effects  of  pain,  but  that  they  actually 
suffer  more  pain. 

Two  modifications  of  cutaneous  sensibility,  itching  and 
tickling,  deserve  particular  mention.  Neither  is  clearly 
explained,  but  it  would  appear  that  itching  is  never  a 
normal  nerve  impulse,  but  is  always  the  result  of  in- 
jury or  disease;  while  tickling  seems  to  be  a  modifica- 
tion of  tactile  sensation  due  to  rapidly  repeated  stim- 
ulation. Some  observers  think  itching  a  mild  stimula- 
tion of  nerves  conveying  painful  sensation. 

The  function  of  the  mammary  gland  will  be  described 
with  the  reproductive  organs. 


CHAPTER  VIII 

THE  DUCTLESS  GLANDS 

The  glands  the  functions  of  which  have  been  studied 
have  ducts  which  carry  the  results  of  their  labor  to  the 
point  at  which  it  is  to  be  used  in  the  animal  economy. 
There  remain  a  number  of  glandular  organs,  with  no 
ducts,  which,  nevertheless,  exert  a  great  influence  on 
the  vital  changes  of  the  body,  in  some  instances  being  of 
such  power  that  their  removal  is  followed  by  death 
within  a  brief  period  of  time. 

These  glands  are  the  thyroid,  with  its  accompanying 
parathyroids,  situated  on  the  trachea  near  the  root  of 
the  neck ;  the  thymus,  located  in  front  of  the  great  ves- 
sels just  above  the  heart ;  the  adrenal  bodies,  or  supra- 
renal capsules,  perched  on  the  top  of  each  kidney;  the 
pituitary,  located  at  the  base  of  the  brain  in  a  peculiar 
depression  of  the  skull  called  sella  turcica;  the  pineal 
gland  imbedded  in  the  brain  substance  near  the  con- 
necting link  between  the  third  and  fourth  ventricles ;  and 
the  spleen  in  the  abdominal  cavity,  the  largest  of  all  the 
ductless  glands.  The  secretion  of  each  of  these  glands 
is  poured  directly  into  the  current  of  the  blood  and  acts 
through  that  organ.  It  is  designated  an  internal  secre- 
tion because  there  is  no  obvious  apparatus  for  its  dis- 
charge. Some  of  the  work  done  by  glands  with  ducts, 
like  the  formation  of  urea  by  the  liver,  partakes  of  the 
nature  of  internal  secretion.  Like  the  secretin,  noticed 
in  the  discussion  of  digestion,  these  internal  secretions 

94 


THE   DUCTLESS    GLANDS 


95 


excite  activity  in  other  organs,  except  in  a  few  cases 
where  they  inhibit  such  activity.  They  have,  therefore, 
been  named  hormones,  meaning  to  excite,  and  chalones 
when  they  inhibit  or  prevent  activity. 


Fig.  21. — The  thyroid  gland.      (Gray's  Anatomy,  after  Spalteholz.) 

While  no  adequate  explanation  of  the  function  of  the 
thyroid  and  parathyroids  can  be  given,  it  seems  clear 
that  the  former  forms  a  hormone  which  stimulates  other 


96  PHYSIOLOGY   FOR   NURSES 

tissues  and  increases  their  metabolism;  i.e.,  the  process 
by  which  living  cells  incorporate  substances  taken  from 
blood  into  parts  of  their  own  bodies,  a  sort  of  cellular 
digestion  or  rather  building  up.  Feeding  thyroid  extract 
will  cause  an  increase  in  the  output  of  nitrogen  and  an 
increase  in  the  oxidation,  or  burning  up,  of  fat,  That 
the  gland  is  intimately  connected  writh  nutrition  is  shown 
by  the  production  of  idiocy  and  arrested  growth  when  it 
atrophies  in  the  young.  The  parathyroids  are  even  less 
understood.  Their  complete  removal  causes  rapid 
death.  That  they  are  connected  with  the  metabolism  of 
calcium  (lime)  salts,  seems  clear.  When  the  thyroid 
fails  to  develop  in  early  childhood,  a  condition  called 
cretinism  occurs,  in  which  there  is  a  failure  to  grow  in 
height  or  intelligence.  In  fact  the  person,  though  reach- 
ing adult  life,  remains  an  idiotic  dwarf. 

Removal  of  the  parathyroids  results  in  a  condition  of 
tetany.  muscular  tremors,  which  end  fatally  after  pro- 
ducing convulsive  movements  especially  of  the  respir- 
atory muscles.  The  condition  is  called  liypotJiyroidism 
and  may  be  relieved  by  calcium  salts. 

Hyperthyroidism  is  produced  by  overactivity  of  the 
thyroid  and  is  attended  by  nervousness,  muscular  wast- 
ing, weakness  and  protrusion  of  the  eyeballs,  from 
which  symptom  the  name  exoplitlialmic  goiter  has  been 
derived. 

The  active  principle  of  the  adrenal  bodies  is  called 
epinephrine  (the  trade  name  of  which  is  adrenalin) 
which  slows  the  heart  ultimately  by  acting  reflexly 
through  the  central  nervous  system,  and  at  the  same 
time  causes  a  great  rise  in  blood  pressure  by  exciting 
constricton  of  the  arterioles.  It  also  seems  to  affect  car- 


THE   DUCTLESS    GLANDS  97 

bohydrate  metabolism.  While  so  little  can  be  said  oi  the 
exact  functions  of  the  adrenal  bodies,  their  importance 
in  our  economy  is  obviously  immense,  since  their  entire 
removal  always  ends  fatally. 

Nothing  need  be  said  of  the  thymus  except  that  its 
partial  atrophy  and  disappearance  at  puberty  indicates 
that  it  is  connected  with  the  development  of  the  organs 
of  reproduction. 

The  pituitary  consists  of  lobes  having  different  func- 
tions, if,  indeed,  they  are  not  separate  glands.  The  hor- 
mone of  the  anterior  lobe  presides  over  and  stimulates 
growth  of  the  skeleton  and  perhaps  all  connective  tis- 
sues; while  that  of  the  posterior  lobe  seems  directed  to 
the  activity  of  some  glands  and  to  preside  over  the  gly- 
cogen  store  in  the  liver  which  it  appears  to  dole  out  in 
appropriate  measure.  An  extract  of  the  pituitary  body 
called  pituitrin  excites  contraction  of  plain  muscle  fiber, 
so  especially  marked  in  the  uterus  that  it  has  been  used 
in  obstetric  work  to  augment  uterine  power. 

Of  the  pineal  body  too  little  is  known  positively  to 
justify  a  statement  of  its  functions,  though  possibly 
they  are  concerned  with  growth. 

In  the  pancreas  certain  masses  are  found  called  is- 
lands of  Langerhans.  There  is  some  evidence  that  these 
furnish  an  inhibitory  chalone  which  prevents  the  too 
rapid  use  of  the  glycogen  in  the  liver. 

Not  a  great  deal,  it  must  be  confessed,  is  positively 
known  about  the  function  of  the  ductless  glands.  But 
there  is  at  least  enough  undisputed  to  warrant  the  as- 
sertion that  they  are  of  very  great,  and,  until  recently, 
of  unsuspected  importance  in  the  general  work  of  keep- 
ing in  repair  and  regulating  many  of  the  most  essential 
organs.  When  the  removal  of  an  organ  weighing  only 


98  PHYSIOLOGY   FOR   NURSES 

a  few  grains  produces  such  changes  that  an  animal 
wastes  away  and  dies,  its  vital  necessity  is  demon- 
strated. To  state  then  that  we  can  not  explain  its  mode 
of  action  does,  indeed,  expose  our  ignorance,  but  does 
not  lessen  the  need  which  our  bodies  have  of  the  organ 
in  question. 


CHAPTER  IX 

THE  NERVOUS  SYSTEM 

The  nervous  system  may  be  compared  to  the  tele- 
phone system  of  a  large  community — the  brain  repre- 
senting the  central  office,  where  calls  are  answered  and 
connections  made;  the  spinal  cord  corresponding  to  the 
large  cables  conducting  the  mass  of  wires  to  and  from 
the  office,  the  peripheral  nerves  to  the  wires  of  the  in- 
dividual subscribers.  The  analogy  is,  of  course,  imper- 
fect, but  serves  the  same  purpose  as  a  diagrammatic 
drawing.  Nerves  carrying  impulses  from  the  periphery 
to  center  are  like  wires  running  from  individual  to  cen- 
tral ;  while  those  which  run  to  muscles,  glands,  etc., 
would  resemble  wires  running  to  the  individuals  called, 
after  the  connection  has  been  made — central  in  this  in- 
stance resembling  the  function  of  a  nerve  cell  in  a  re- 
flex arc  in  its  simplest  form — i.e.,  an  afferent  nerve  pass- 
ing to  a  cell  and  an  efferent  nerve  from  another  con- 
nected cell  to  periphery.  Such  an  arc  w^ould  be  com- 
plete if  we  conceive  of  an  organism  possessed  of  a  skin 
with  a  sensory  nerve,  a  muscle  to  move  the  organism,  a 
nerve  cell  to  respond  to  an  appeal  from  the  surface  and 
a  nerve  fiber  from  cell  to  muscle.  If  we  imagine  that 
such  an  organism  encounters  something  painful,  the 
course  of  the  nerve  impulse  would  be  from  the  nerve 
ending  in  the  skin  to  the  cell,  where  the  danger  is  rec- 
ognized and  an  order  sent  along  the  efferent  nerve  to 
the  muscle  to  contract  and  remove  the  organism  from 
daner. 


100 


PHYSIOLOGY   FOR   NURSES 


The  elements  of  the  central  nervous  system  are  the 
brain,  divided  into  the  two  hemispheres  of  the  cerebrum, 
two  crura,  connecting  links  between  the  cerebrum  and 
the  lower  portions  of  the  nervous  system,  the  pons,  the 
medulla  or  ~bulb,  the  two  hemispheres  of  the  cerebellum 
and  the  spinal  cord.  All  of  these  component  parts,  ex- 
cept the  last,  are  found  in  the  skull,  enclosed  in.  the 
three  membranes  of  the  brain,  while  the  cord,  also  en- 
closed in  three  similar  membranes,  continuous  with 


Fig.  22. — Schema  of  simple  reflex  arc:  r,  receptor  in  an  epithelial  mem- 
brane; a,  afferent  fiber;  s,  synapsis;  c,  nerve  cell  of  center;  e,  efferent  fiber; 
m,  effector  organ.  (Pearce-Macleod,  Fundamentals  of  Human  Physiology.) 

those  of  the  brain,  is  in  the  spinal  canal  which  runs 
through  the  vertebral  column. 

The  peripheral  nervous  system  is  made  up  of  the  cra- 
nial and  spinal  nerve  trunks  and  ganglia  and  their  nu- 
merous endings  in  various  parts  of  the  body. 

The  sympathetic  system  is  a  chain  of  ganglia  and  con- 
necting fibers  situated  on  each  side  of  the  spinal  col- 
umn, connected  with  both  cranial  and  spinal  nerves,  and 
witie 


102  PHYSIOLOGY  FOE   NURSES 

A  broad  view  of  the  entire  nervous  system  reveals 
that  the  brain  is  the  highest  development  of  the  system, 
presiding  over  the  work  of  the  rest,  thinking,  ordering, 
and  governing  through  its  subsidiaries.  Some  of  its 
impressions  are  received  directly,  and  some  of  its  orders 
given,  through  the  medium  of  the  cranial  nerves;  but 
from  the  larger  portion  of  the  body  its  various  ssnsa- 
tions  and  actions  must  be  transmitted  to  the  brain 
through  the  spinal  cord.  In  this  transmission  the  cord, 
like  a  good  subordinate  officer,  finds  many  things  of 
such  simple  and  routine  nature  that  the  conscious  brain 
need  not  be  troubled  with  them  and  itself  interprets  the 
information  and  gives  the  necessary  instructions.  Thus 
it  appears  that  while  much  of  the  tissue  of  the  cord  is 
solely  employed  in  conducting  impulses  to  or  from  the 
periphery  of  the  body,  it  is  capable  of  action,  not  ab- 
solutely independent,  but  under  general  orders  of  the 
brain. 

The  sympathetic,  or  more  properly  autonomic  system 
is  much  more  independent.  While  connected  with  the 
brain  and  spinal  cord,  its  functions  are,  in  large  meas- 
ure, performed  without  the  conscious  will  of  either. 

The  Cerebral  Hemispheres. — In  these  subdivisions  of 
the  fore  brain  we  find  the  higher  centers.  Here  reside 
those  intellectual  functions  which  we  are  thinking  of 
when  we  say  "we 'think."  In  that  part  of  the  cortical 
matter — like  bark,  surrounding  other  matter — whicli  is 
found  over  the  anterior  part  of  the  frontal  lobe  probably 
originate  the  highest  philosophic  conceptions;  in  front 
of  the  central  sulcus  (fissure  of  Rolando)  lies  the  long 
area  stretching  from  the  top  to  near  the  bottom  of  the 
brain  which  presides  over  all  motor  activity,  with  the 
special  centers  for  the  lower  extremity  at  the  top,  those 
for  the  upper  extremity  in  the  middle  and  for  the  face 


THE   NERVOUS   SYSTEM  103 

at  the  bottom.  Behind  the  same  fissure  lies  an  area  of 
nearly  like  size  and  shape  which  receives  and  interprets 
those  sensations  communicated  from  the  periphery,  like 
pain,  pressure,  heat  and  cold,  which  were  discussed  with 
the  skin.  Around  the  end  of  the  Sylvian  fissure  is  an 
angular  area  concerned  in  word  and  object  seeing.  Just 
below  the  same  fissure  lies  the  center  for  hearing  and 
one  still  lower  for  the  interpretation  of  words.  In  the 


Fig.  24. — Cortical  centers  in  man.  Of  the  three  shaded  areas  bordering  on 
the  Rolandic  fissure  (hoi.),  the  most  anterior  is  the  precentral  associational 
area,  the  middle  one  is  the  motor  area  (the  position  of  the  body  areas  are 
indicated  on  it),  and  the  ma,st  posterior  is  the  sensory  area,  to  the  cells  of 
which  the  fillet  fibers  proceed.  The  centers  for  seeing  and  hearing  are  also 
shown.  The  unshaded  portion  in  front  cf  the  Rolandic  area  is  the  precentral; 
the  portions  behind,  the  parietal  and  temperosphenoidal.  (Pearce-Macleod, 
Fundamentals  of  Human  Physiology.) 

occipital  lobe  is  the  center  for  vision,  while  the  centers 
for  smelling  and  tasting,  closely  associated,  appear  to 
be  on  the  inner  surface  of  the  temporosphenoidal  lobe 
near  its  anterior  end.  A  glance  at  the  surface  of  the 
brain,  or  a  good  picture  of  the  cortex,  will  show  how 
small  a  surface  is  employed  in  the  functions  of  motion 


104 


PHYSIOLOGY   FOR   NURSES 


and  in  receiving  sensations  from  the  skin  and  tissues. 
This  indicates  that  the  amount  employed  in  the  mere 
sensations  of  seeing,  hearing,  tasting  and  smelling  is 
equally  small,  and  that  the  remainder  of  the  cortex,  a 
very  large  portion  of  the  whole,  must  be  occupied,  as 
association  areas  in  analyzing  the  sensations  brought  in 


I  Corpus 


callosum 


— Vision 


Olfactory 
gustatory 


Pens] 
Medulla  oblongatal 

Fig.    25. — Brain,   mesial  view. 


— Cerebellum 


by  these  highly  trained  and  developed  nerves.  Thus, 
the  uneducated  may  see  a  word  as  distinctly  as  the 
trained,  but  it  conveys  no  meaning,  any  more  than  would 
a  word  in  an  unknown  tongue.  We  can,  therefore,  read- 
ily comprehend  that  we  have  not  only  memory  for  words 
and  their  definitions,  but  that  special  areas  of  the  brain 
may  be  taught  to  preside  over  these  functions  and  so 
associate  certain  characters,  which  we  call  letters,  with 


THE    NERVOUS   SYSTEM  105 

a  certain  meaning,  when  combined  in  a  definite  way, 
which  always  conveys  the  same  idea  to  one's  mind.  Edu- 
cation, therefore,  would  be,  in  this  sense,  simply  the 
formation  of  certain  habits;  and  as  the  frequent  repeti- 
tion of  the  same  act  leaves  each  time  a  firmer  impress  on 
the  mind,  the  habit  may  finally  become  automatic  and  be 
performed  without  definite  consciousness.  As  the 
thoughts  of  at  least  a  large  majority  of  mankind  are  al- 
ways dependent  on  sensations  received  from  without,  it 
is  apparent  that  without  the  association  areas  the  high- 
est intellectual  functions,  which  are  entirely  dependent 
on  such  associations,  can  not  be  performed;  and  it  fol- 
lows that  disturbance  in  any  of  the  areas,  or  in  the  con- 
ducting paths  which  lead  between  them,  may  give  rise 
to  an  interruption  of  function,  or  at  least  such  a  dis- 
turbed condition,  that  connected  thought  becomes  im- 
possible. Temporarily  such  an  interruption  occurs  in 
the  delirium  of  illness  and  permanently  in  various  types 
of  insanity.  Neither  is  it  surprising  that  parts  of  an 
area  alone  may  be  affected.  Thus  a  symptom  of  "word 
blindness"  may,  and  does  occur  in  which  there  is  a  com- 
plete failure  to  recognize  printed  or  written  words 
though  speech  is  not  affected. 

The  association  areas  referred  to  must  not  be  con- 
founded with  those  fibers — the  corpus  callosum — which 
run  between  the  two  halves  of  the  cerebrum  and  associ- 
ate, or  coordinate,  the  action  of  similar  centers,  for  ex- 
ample, make  the  centers  for  the  two  upper  extremities 
act  in  concert,  as  in  swimming. 

The  most  widely  scattered,  and  one  of  the  most  im- 
portant, association  areas  is  that  called  the  "language 
area."  In  order  that  the  fullest  use  may  be  made  of  a 
language,  it  must  be  spoken,  heard,  written  and  read. 
This  necessitates  not  only  the  highly  specialized  nerves 


106  PHYSIOLOGY   FOR   NURSES 

of  vision  and  hearing,  but  the  use  of  all  muscles  in- 
volved in  uttering  articulate  sounds,  moving  the  eye- 
balls in  unison  or  the  hand  in  Avriting,  and  the  centers 
for  each  must  not  only  be  associated  with  each  other, 
but  each  in  turn  must  be  closely  connected  with  those  cen- 
ters which  originate  the  thought  to  be  expressed,  select 
words  with  the  proper  shade  of  meaning,  or  comprehend 
the  full  meaning  of  a  writer  or  speaker;  while  the  sen- 
sory nerves  of  lips  and  tongue  must  also  be  in  harmony. 
The  area  involved,  therefore,  would  be  large  segments 
of  the  frontal,  parietal,  occipital  and  temporosphenoidal 
lobes.  Probably,  too,  special  sections  are  devoted  to 
musical  sense,  associated  with  language,  at  least  in  vo- 
cal music,  since  we  find  some  children  devoid  of  all  ideas 
of  music  while  others,  at  an  equally  early  age,  have  what 
wo  call  a  "good  ear"  for  musical  sounds. 


THE  CRURA,  PONS,  CEREBELLUM,  MEDULLA 

Our  knowledge  of  the  remaining  segments  of  the 
brain  is  neither  so  extensive  nor  so  definite  as  that  which 
we  possess  of  the  cerebrum. 

The  crura  cerebri  are  in  the  main  composed  of  white 
fibers  which  convey  nerve  impulses  to  and  from  the  cor- 
tex through  the  pons  to  the  medulla,  and  thence  to  the 
spinal  cord;  though  they  contain  gray  matter  supposed 
to  be  concerned  in  coordinating  the  movements  of  the 
eyeball  and  iris. 

The  pons  consists,  superficially,  of  transverse  fibers 
which  connect  the  hemispheres  of  the  cerebellum  with 
each  other  and  deeply  of  longitudinal  fibers,  derived 
from  the  crura,  running  to  the  medulla.  It  may  assist 
in  regulating  automatic  voluntary  movements  (Flint). 

The  corpora  striata  and  optic  thalami  are  masses  of 


THE    NERVOUS    SYSTEM  107 

gray  matter  imbedded  in  the  cerebrum,  the  first  inti- 
mately connected  with  the  anterior  part  of  the  internal 
capsule  and  the  latter  with  its  posterior  third.  Since 
these  bundles  carry  respectively  motor  (efferent)  and 
sensory  (afferent)  impulses,  the  corpora  are  supposed 
to  be  connected  with  motion  and  the  thalami  with  sen- 
sation. 

Four  small  bodies — corpora  quadrigemina — are  sit- 
uated just  back  of  the  thalami.  The  first  pair  are  con- 
nected with  vision  and  the  posterior  with  hearing. 

The  cerebellum  is  so  much  larger  than  the  portions  of 
brain  just  discussed  that  mere  size  would  indicate  its 
possession  of  important  functions.  We  are,  however,  al- 
most entirely  ignorant  of  its  work  and  so  many  theories 
have  been  advanced  that  one  hesitates  to  speak  of 
knowledge  of  the  subject.  Its  removal  certainly  causes 
a  loss  of  the  power  of  coordinating  voluntary  muscular 
action  in  animals;  so  that  if  a  coordinating  center  for 
this  purpose  exists,  it  is  highly  probable  that  it  is  located 
in  the  cerebellum,  and  aids  in  maintaining  equilibrium. 

The  Medulla  Oblongata. — Here  we  are  on  firmer 
ground.  This  somewhat  pear-shaped  body  seems  to  con- 
tinue the  conducting  fibers  from  all  parts  of  the  brain 
lying  above  it  into  the  spinal  cord.  Its  conducting  func- 
tion, a  large  part  of  its  work,  is,  therefore,  obvious.  The 
paths  of  conduction  of  motor  impulses  are  in  the  an- 
terior pyramids,  whose  fibers  cross  to  the  opposite  side 
of  the  cord  as  the  crossed  pyramidal  tracts — explaining 
why  an  injury  to  the  motor  area  of  one  Cerebral  hemi- 
sphere causes  paralysis  of  the  other  side  of  the  body. 

The  sensory  fibers  finally  pass  through  the  medulla 
into  that  region  of  the  cord  around  the  posterior  roots 
of  the  spinal  nerves  with  which  they  are  connected. 


108  PHYSIOLOGY   FOR   NURSES 

They  do  not  all  cross  at  one  point,  but  successively  as 
they  pass  down  the  spinal  cord. 

The  medulla  is  an  important  reflex  nerve  center  dif- 
fering somewhat  from  a  similar  action  of  the  cord  which 
will  be  discussed  later. 

Respiratory  Center. — Among  these  centers  that  pre- 
siding over  respiration  is  so  important  that  the  point  at 
which  it  is  located  has  long  been  called  the  ' '  vital  spot. ' ' 
To  carry  on  a  function  so  essential  as  breathing,  a  mech- 
anism must  be  employed  which  can  act  independently  of 
the  will,  which  functions  when  one  is  asleep  or  uncon- 
scious— as  in  anesthesia.  This  center  is  located  in  the 
lower  part  of  the  medulla  and  consists  of  two  parts,  one 
on  each  side  of  the  midline,  each  presiding  over  its  own 
side  of  the  body.  Its  neurons  descend  in  the  spinal  cord 
and  are  connected  through  the  gray  matter  witli  the 
spinal  nerves  at  their  points  of  origin  at  different  levels. 
Motor  impulses,  therefore,  originate  in  the  medullary 
center  and  are  distributed  to  the  lower  centers  in  the 
cord,  or  to  the  centers  of  the  vagus  or  facial  nerve.  Es- 
sentially the  center  is  automatic  and  is  normally  stim- 
ulated by  the  amount  of  carbon  dioxide  in  the  blood ;  i.e., 
if  the  amount  of  C02  is  small,  the  respirations  will  be 
fewer,  if  the  amount  is  increased  the  respiratory  move- 
ments will  increase  in  number.  This  fact,  and  the  ex- 
tent of  the  control  which  the  brain  exerts  over  the  cen- 
ter, is  illustrated  in  "holding  the  breath."  One  may 
voluntarily  cease  to  breathe  for  a  time,  but  when  C02 
has  sufficiently  accumulated  in  the  venous  blood  in  the 
center,  an  inspiration  takes  place  regardless  of  one's 
attempts  to  prevent  it. 

The  chief  motor  (efferent)  nerve  which  carries  the  im- 
pulses of  the  center  is  the  phrenic,  a  branch  of  the  cer- 
vical plexus,  though  the  intercostal,  lumbar  and  other 


THE   NERVOUS   SYSTEM  109 

nerves  also  play  an  important  part.  The  sensory  nerve 
chiefly  concerned  is  the  tenth  cranial  or  vagus  which  is 
in  part  distributed  directly  to  the  lung  tissue,  but  al- 
most any  sensory  nerve  may  convey  impulses  to  this 
center.  The  vagus  appears  to  carry  two  sets  of  fibers, 
inspiration  stimulating  the  inhibitory  fibers  by  expan- 
sion of  the  lung,  while  the  partial  collapse  of  the  lung  at 
expiration  stimulates  the  inspiratory  fibers.  That  the 
sensory  nerves  of  the  skin  affect  the  center  anyone  may 
prove  by  dashing  cold  water  over  the  person  and  noting 
the  "gasp  for  breath"  which  immediately  follows.  The 
sensory  nerves  of  the  face,  breathing  and  swallowing 
passages  (fifth  and  ninth)  can  inhibit  inspiration.  This 
is  a  protective  arrangement  whose  action  can  be  shown 
by  swallowing  when  the  reflex  through  the  ninth  tem- 
porarily arrests  respiratory  movements;  by  breathing 
or  attempting  to  breathe,  any  irritating  gas,  like  am- 
monia, the  inhibitory  impulses  in  this  case  following  the 
fibers  of  the  fifth  in  the  nose. 

At  birth  the  first  inspiration  of  the  newborn  child 
seems  to  be  caused  mainly  by  the  accumulation  of  C02 
in  the  infant's  blood  as  a  result  of  cutting  off  its  connec- 
tion with  the  mother  through  the  placenta;  though  a 
contributing  stimulation  is  the  exposure  of  the  skin, 
with  its  sensory  nerves,  to  the  air.  Obstetricians  must 
often  take  advantage  of  this  to  start  the  inspirations 
which  do  not  always  begin  at  once  after  prolonged  and 
difficult  labor. 

Apnea  and  Dyspnea. — The  first  of  these  terms  means 
absence  of  breathing  literally,  but  is  employed  in  physi- 
ology to  describe  a  condition  of  respiratory  rest  when 
the  lungs  and  blood  are  full  of  oxygen.  A  fleeting  con- 
dition of  apnea  is  produced  by  a  very  full  inspiration. 

Dyspnea,  difficult  or  labored  breathing,  is  the  condi- 


110  PHYSIOLOGY  FOR   NURSES 

tion  produced  by  a  marked  increase  of  carbon  dioxide 
or  a  similar  decrease  in  oxygen.  It  could  be  produced 
by  diminishing  the  amount  of  oxygen  in  the  respired 
air,  by  blocking  up  the  air  passages,  as  by  choking,  or 
decreasing  available  lung  space.  When  carried  to  ex- 
cess as  by  hanging,  a  condition  of  aspliyxia  results. 

The  vagus  nerve  carries  two  sets  of  fibers  to  the  mus- 
cles of  the  bronchioles — those  which  excite  contraction 
when  stimulated,  and  those  which  cause  dilatation.  They 
are  called  broncho  constrict  or  and  bronclwdilator  fibers. 

Cardiac  Center. — This  center  is  found  in  the  neighbor- 
hood of  the  roots  of  the  vagus  nerve,  through  which  it 
exerts  a  slowing  and  regulating  influence  on  the  heart- 
beats, and  is,  therefore,  called  the  cardioinhibitonj  cen- 
ter. Whether  there  be  a  distinct  accelerating  center  in 
the  medulla  is  disputed.  It  is  certain  that  nerve  fibers 
sent  to  the  heart  by  the  sympathetic  system  increase  the 
rate  of  the  heartbeat.  Other  nerves  affect  the  action  of  the 
heart  reflexly.  Painful  sensations,  particularly  from  the 
viscera,  slow  the  heart,  These  sensations  are  carried 
into  the  central  nervous  system  and  act  reflexly  on  the 
inhibitory  center  stimulating  it  to  greater  activity.  On 
the  other  hand,  emotion  may  stimulate  the  accelerator 
center  and  cause  a  more  rapid  beat,  sometimes  attended 
by  less  power.  Hence  it  has  been  inferred  that  acceler- 
ator nerves  carry  two  sets  of  fibers,  one  simply  to  in- 
crease the  rate  of  action  of  the  heart  and  the  other  to 
augment  its  power.  Fear,  therefore,  might  increase  the 
rapidity  with  loss  of  strength,  while  anger  could  aug- 
ment both. 

Vasomotor  Center. — The  action  of  the  blood  vessels 
consists  in  dilating  to  increase  and  constricting  to  di- 
minish their  capacity. 

A  vasoconstrictor  center  in  the   medulla  is  demon- 


THE   NERVOUS   SYSTEM 


111 


strated,  but  there  seems  to  be  no  vasodilator  center. 
Changes  in  the  size  of  the  blood  vessels  are  caused  by 
the  constriction  of  the  muscular  coat  to  reduce  the  size 
and  relaxation  to  increase  size.  Constriction  dimin- 
ishes and  dilatation  increases  the  quantity  of  blood  in 
the  area  of  distribution  of  the  vessels  involved.  The  im- 
pulses are  carried  by  the  sympathetic  autonomic  sys- 


Fig.  26. — Diagram  of  section  of  spinal  cord,  showing  tracts.  (After  K61- 
liker)  ;  g,  posterior  median,  and  b,)  postero-lateral  columns;  p.c.,  crossed 
pyramidal,  and  p.d.,  direct  pyramidal  tracts;  f,  cerebellar  tract.  (After 
Ho  well.) 

tern  and  are  not  under  the  control  of  the  conscious  will, 
though  the  higher  centers  of  the  brain  can  excite  them 
as  may  be  seen  in  blushing — a  vasodilatation  of  the  ves- 
sels of  the  face.  Ordinarily  the  center  is  excited  re- 
flexly,  as  when  exposure  to  cold  causes  a  constriction  of 
the  vessels  in  the  part  affected.  Fright,  grief,  the  recep- 
tion of  bad  news  may  cause  the  temporary  unconscious- 


112  PHYSIOLOGY   FOR   NURSES 

ness  called  fainting  by  inhibiting  the  constrictor  center 
and  allowing  such  dilatation  of  the  great  venous  chan- 
nels, particularly  those  of  the  abdomen,  that  there  is  too 
little  blood  in  the  brain  to  maintain  its  normal  state. 
Nature  indicates  the  remedy  by  throwing  the  fainting 
person  down. 

Parts  of  the  medulla  are  supposed  to  contain  various 
other  centers,  such  as  for  the  control  of  salivary  secre- 
tion, swallowing,  vomiting,  etc. 

The  Spinal  Cord.— Like  other  parts  of  the  central 
nervous  system,  the  spinal  cord  consists  of  gray  and 
white  matter,  the  gray  being  in  the  center  and  the  white 
on  the  outside,  a  converse  arrangement  to  that  of  the 
brain.  While  mainly  employed  in  conducting  impulses 
to  and  from  the  brain,  the  cord  contains  many  reflex 
centers  more  or  less  under  the  control  of  the  higher  cen- 
ters. 

The  fissures  on  the  front  and  back  of  the  cord  indi- 
cate a  partial  subdivision  into  hemispheres,  similar  to 
ihe  subdivision  of  the  cerebrum,  while  the  large  mass 
stretching  from  one  half  to  the  other  suggests  the  pres- 
ence of  commissural  fibers  connecting  and  coordinating 
the  two.  The  gray  matter,  projected  in  the  form  of  ir- 
regular horns  into  the  front  and  back  of  each  half  of  the 
cord,  contains  the  cells,  the  branches  of  which  connect 
on  the  one  hand  with  the  fibers  of  the  entering  nerves 
and  on  the  other  with  branches  of  other  cells  in  turn  con- 
nected with  the  fibers  of  nerves  leaving  the  cord  either 
on  the  same  or  the  opposite  side.  Such  an  arrangement 
completes  the  formation  of  a  reflex  arc,  composed  of  a 
nerve  fiber  connecting  a  sensory  terminal  with  the  re- 
ceiving branch  of  the  cell  in  the  gray  column,  the  dis- 
patching branch  of  which  connects  with  the  receiving 
branch  of  a  cell  in  the  motor  area,  the  dispatching  branch 


Fig.  27. — The  simplest  reflex  arc  in  the  spinal  cord.  (After  Kolliker.) 
The  afferent  fiber  in  the  posterior  root  (in  black)  gives  off  collaterals,  which 
end  by  synapses  around  the  cells  of  the  anterior  horn  (in  red),  the  axons 
of  which  form  the  efferent  fibers  of  the  anterior  roots.  (Howell's  Physi- 
ology.) 


THE   NERVOUS    SYSTEM  113 

of  which  in  turn  joins  a  departing — motor  or  secretoi-y— 
fiber,  the  peripheral  termination  of  which  is  in  the  muscle 
or  gland  which  is  to  receive  the  stimulus  to  activity. 
Moreover  there  are  ascending  branches  connected  with 
similar  cells  which  put  the  entire  arc  in  communication 
with  the  brain,  and  radiating  branches  which  form  con- 
nections with  other  sensory  and  motor  centers,  so  that  all 
may  be  under  the  control  of  the  higher  centers  and  all 
coordinated  with  each  other. 

The  conducting  fibers  for  descending  impulses — effer- 
ent— cross  at  the  lower  part  of  the  medulla  and  form  the 
anterior  pillars  or  columns  of  the  cord.  The  ascending 
impulses  are  carried  in  the  posterior  columns  and  cross 
at  various  levels  as  they  ascend,  though  many  cross  in 
the  lower  part  of  the  medulla  forming  the  posterior  or 
sensory,  decAissation.  Other  afferent  fibers  are  con- 
nected with  lateral  tracts  of  the  cord,  near  the  entrance 
of  the  posterior  roots  of  the  spinal  nerves,  and  are  car- 
ried through  the  restiform  bodies  of  the  medulla  into 
the  cerebellum  on  the  same  side.  Apparently  the  paths 
in  the  cord  along  which  tactile  impressions  are  carried 
are  not  the  same  as  those  traveled  by  pain  and  temper- 
ature sensations,  as  indicated  by  a  disease  in  which  there 
is,  in  affected  regions,  loss  of  the  power  of  feeling  pain 
or  detecting  differences  in  temperature,  while  the  pres- 
sure sense  is  not  affected ;  but  these  paths  are  not  clearly 
defined. 

As  the  motor  fibers  all  decussate  (cross  to  the  oppo- 
site side)  near  the  junction  of  the  medulla  and  cord,  and 
many  of  the  sensory  fibers  are  crossing  all  the  way  from 
the  entrance  of  the  sensory  roots  upward,  injury  to  one- 
half  of  the  cord  will  produce  total  motor  paralysis  of 
the  same  side  and  partial  sensory  paralysis  of  the  same 
side,  but  all  sensation  is  not  abolished  below  the  injury. 


114  PHYSIOLOGY   FOR   NURSES 

Injury  to  the  area  of  the  surface  matter  of  the  brain 
governing;  these  paths  causes  both  motor  and  sensory 
paralysis  of  the  opposite  side,  because  all  the  fibers  of 
both  kinds  cross  before  reaching  the  origin  of  the  spinal 
nerves  which  convey  these  impulses  to  or  from  the  tis- 
sues. 

Centers  of  the  Spinal  Cord. — There  are  two  enlarge- 
ments of  the  spinal  cord,  one  situated  in  the  cervical  and 
the  other  in  the  lumbar  portion.  While  these  ''second- 
ary brains"  can  not  be  located  with  exactness,  there  is 
sufficient  evidence  to  show  that  the  cervical  enlargement 
contains  groups  of  cells  or  centers  which  preside  over 
the  movements  of  the  upper  extremity,  accelerate  the  ac- 
tion of  the  heart,  cause  dilatation  of  the  pupil,  and  reg- 
ulate or  prescribe  the  activity  of  the  cervical  sympa- 
thetic system  of  nerves.  There  is  here  also  a  spinal  res- 
piratory center. 

In  the  lumbar  enlargement  are  centers  controlling  the 
rectum,  bladder  and  the  genital  organs  and  the  move- 
ments of  the  lower  limbs. 


THE  CRANIAL  AND  SPINAL  NERVES 

The  cranial  nerves — twelve  pairs — differ  from  the 
spinal  in  being  directly  attached  to  some  part  -  of  the 
brain  and,  usually,  in  carrying,  in  each  pair,  either  af- 
ferent or  efferent  fibers  alone.  They  are  known  by  num- 
bers from  before  backwards  and  also  have  synonyms  in- 
dicating their  function.  The  first,  or  olfactory;  second 
or  optic;  eighth,  or  auditory;  and  ninth,  or  glosso- 
pharyngeal,  are  concerned  with  smelling,  seeing,  hear- 
ing and  tasting  and  are  described  with  the  organs  of 
special  sense. 

The  third,  or  motor  oculi;  fourth,  or  patheticus;  and 


THE   NERVOUS   SYSTEM  115 

sixth  or  abducent  all  carry  motor  impulses  to  the  mus- 
cles which  move  the  eyeball.  Their  function  is,  there- 
fore, sufficiently  indicated  by  their  distribution. 

The  fifth,  or  trifacial,  resembles  a  spinal  nerve  in  ris- 
ing by  a  motor  and  a  sensory  root,  only  the  sensory  is 
in  front  and  the  larger  of  the  two.  It  is  emphatically 
the  neuralgic  nerve,  so  frequently  does  this  painful  af- 
fection attack  the  sensory  branches  of  this  widely  dis- 
tributed nerve.  Its  synonym  of  trifacial  is  derived  from 
its  splitting  into  three  divisions  and  leaving  the  skull  by 
three  openings.  One  division,  the  ophthalmic  conveys 
news  from  the  mucous  membrane  and  part  of  the  skin 
of  the  nose,  the  eyeball  and  lacrimal  gland,  forehead  and 
upper  eyelid;  the  next,  upper  maxillary  (jaw)  is  the 
afferent  nerve  from  the  skin  covering  the  upper  jaw, 
side  of  the  nose,  upper  lip  and  lower  lid  and  from  the 
teeth  and  gum  of  the  upper  jaw  the  tonsils  .and  nasal 
and  throat  mucous  membrane.  The  third  division,  in- 
ferior maxillary,  does  the  same  work  for  the  lower  jaw 
and  its  surroundings,  including  the  tongue  and  salivary 
inlands,  the  skin  at  the  back  of  the  ear  running  to  the 
top  of  the  head,  and  takes  all  the  efferent  fibers  which 
are  distributed  to  the  muscles  which  move  the  lower  jaw. 
The  nerve  resembles  a  spinal  nerve  also  in  possessing 
an  enlargement  called  a  ganglion  on  its  afferent  root  in 
which  these  fibers  arise,  the  branches  or  roots  of  the 
ganglion  furnishing  the  connection  with  the  brain.  This 
arrangement  is  identical  with  that  of  the  spinal  and 
other  cranial  nerves  which  contain  mixed  fibers. 

The  eleventh  and  twelfth,  or  hypoglossal,  nerves  con- 
tain none  but  efferent  (motor)  fibers.  The  eleventh  is 
distributed  to  very  important  muscles  of  the  neck  and 
back  and  is  often  connected  with  the  surgical  affection 
called  wry  neck. 


116  PHYSIOLOGY  FOR   NURSES 

The  twelfth  conveys  efferent  impulses  to  those  mus- 
cles which  depress  the  hyoid  bone,  to  the  tongue  and 
many  of  the  muscles  which  move  that  organ. 

While  the  seventh,  or  facial,  nerve  proper  contains 
none  but  efferent  fibers,  mainly  distributed  to  those 
small  bundles  which  move  the  face  and  change  its  ex- 
pression— hence  muscles  of  expression, — it  is  connected 
with  a  part  intermediate  between  itself  and  the  auditory 
called  chorda  tympani  or  nerve  of  Wrisberg,  which  sup- 
plies the  salivary  glands  with  vasodilator  and  secretory 
fibers.  The  seventh  is  the  nerve  concerned  in  facial 
paralysis. 

The  ninth,  or  glossopharyngeal,  is  also  a  mixed  nerve. 
The  motor  fibers  are  distributed  to  the  muscles  of  the 
pharynx  and  base  of  the  tongue,  while  secretory  fibers 
are  carried  to  the  parotid  gland. 

The  sensory  fibers  conduct  impulses  from  part  of  the 
mucous  membrane  of  the  tongue,  the  pharynx,  Eusta- 
chian  tube  and  tympanic  cavity.  The  origin  of  this  nerve 
is  from  the  medulla. 

The  tenth,  vagus  or  pneumogastric,  also  springs  from 
the  medulla  just  below  the  ninth  and  is,  like  it,  a  mixed 
nerve.  It  is  the  most  widely  distributed  of  all  the  cra- 
nial nerves,  some  of  its  branches  reaching  such  function- 
ally different  organs  as  the  larynx,  heart,  lungs,  stom- 
ach, and  intestines,  even  so  far  as  the  large  intestine. 
The  motor  (efferent)  fibers  go  to  the  intrinsic  muscles 
of  the  larynx,  while  others  go  to  the  plain  muscles  of 
the  digestive  tract,  including  part  of  the  large  intestine ; 
while  the  afferent  fibers  bring  sensory  impulses  from  the 
mucous  membrane  of  the  larynx,  trachea  and  lungs, 
esophagus,  stomach,  intestines,  gall  bladder  and  its 
duct.  The  nerve  carries  inhibitory  fibers  to  the  heart 
and  secretory  fibers  to  the  pancreas  and  the  glands  of 


THE   NERVOUS    SYSTEM  117 

the  stomach.  It  is  the  agent,  therefore,  by  which  the 
voice  is  produced,  the  air  passages  guarded  against  ir- 
ritants and  excited  to  expel  them;  the  heart  regulated, 
glands  of  the  stomach  and  the  pancreas  incited  to  activ- 
ity and  the  musculature  of  the  swallowing  and  digestive 
organs  stimulated  to  perform  their  functions. 

The  spinal  nerves,  unlike  the  cranial,  always  spring 
from  the  spinal  cord  by  two  roots,  an  anterior,  motor, 
connected  with  the  anterior  column  and  adjacent  gray 
horn,  and  a  posterior  sensory  connected  with  the  poste- 
rior columns  and  the  gray  matter  of  the  posterior  horn. 
After  emerging  there  is  formed,  on  the  posterior  root 
only,  a  ganglion  from  whose  cells  the  posterior  root 
really  springs.  This  ganglion  is  the  trophic  center  of 
this  root;  i.e.,  that  mass  of  cells  which  is  so  essential  to 
the  health  and  activity  of  a  tissue  that  without  it  death 
of  the  tissue  and  degeneration  will  occur.  This  is  proved 
by  cutting  one  nerve  between  the  ganglion  and  the  cord 
and  another  between  the  ganglion  and  periphery,  in  the 
latter  case  only  will  the  nerve  degenerate.  Beyond  the 
ganglion  the  two  roots  unite  to  form  the  spinal  nerves 
as  we  dissect  them.  In  all  regions  except  the  thoracic, 
spinal  nerves  thus  formed  communicate  more  or  less  in- 
timately with  one  another  to  form  anatomic  plexuses, 
from  which  the  ultimate  branches  of  distribution  are  de- 
rived. In  these  plexiform  communications  there  is  a  re- 
distribution of  fibers  in  such  a  way  that  some  nerves 
emerge  which  are  entirely  afferent,  some  entirely  effer- 
ent, but  most  are,  like  the  parent  trunks,  mixed.  The 
plexuses  are  cervical,  brackial,  lumbar  and  sacral  and 
coccygeal. 

The  cervical  plexus  supplies  the  skin  over  the  neck, 
upper  part  of  the  chest,  back  of  the  head  and  thorax  and 
muscles  in  the  same  region. 


118  PHYSIOLOGY   FOR   NURSES 

One  branch,  of  more  importance,  is  the  phrenic,  or 
chief  inspiratory  nerve  since  it  carries  motor  impulses 
to  the  most  important  of  the  inspiratory  muscles,  the 
diaphragm. 

The  brachial  plexus  is  largely  devoted  to  the  upper  ex- 
tremity. One  of  its  branches  supplies  the  serratus  mag- 
nusf  an  accessory  respiratory  muscle,  but  most  of  them 
are  mixed  nerves  some  of  the  fibers  of  which  convey  cu- 
taneous sensations  from  all  parts  of  the  upper  extrem- 
ities, while  motor  branches  supply  all  the  muscles  which 
move  this  great  lever,  even  those  muscles  which  spread 
out  over  the  back  and  chest. 

The  thoracic  nerves  run  mainly  between  the  ribs — in- 
tercostal nerves — supplying  motor  impulses  to  the  mus- 
cles of  the  same  name,  which  makes  them  respiratory 
nerves,  while  their  sensory  fibers  convey  cutaneous  sen- 
sations from  the  skin  of  the  thorax  and  a  large  part  of 
the  abdomen.  The  lower  thoracic  nerves  supply  ths 
broad  muscles  of  the  abdomen  and  are  thus  expiratory 
agents. 

The  lumbar  plexus  gives  rise  to  those  nerves  which 
supply  sensation  to  the  skin  from  where  the  last  inter- 
costal leaves  off  to  where  the  sacral  plexus  takes  up  the 
work,  and  motor  impulses  in  the  same  area.  The  first 
of  the  lumbar  nerves  supplies  the  skin  over  the  upper, 
outer  part  of  the  hip  and  others  carry  the  distribution 
over  the  front  and  inner  side  of  the  thigh  and,  by  one 
long  branch,  along  the  inner  side  of  the  leg  as  far  as  the 
big  toe.  The  skin  over  the  external  genitals  is  supplied 
in  part  by  this  plexus.  The  muscles  supplied  are  those 
forming  the  lower  part  of  abdominal  wall,  some  in  the 
back  of  the  abdomen  and  pelvis  and  those  on  the  front 
and  inner  side  of  the  thigh.  Briefly  the  muscles  which 


THE    NERVOUS    SYSTEM  119 

flex  or  adduct  the  thigh  or  extend  the  knee,  receive 
their  impulses  through  the  lumbar  plexus. 

The  sacral  and  coccygeal  nerves  supply  motor  and 
sensory  fibers  to  the  external  genitals,  the  hip,  back  of 
the  thigh  and  all  of  the  leg  and  foot,  except  the  inner 
side  of  these  parts  which  receive  their  supply  from  the 
lumbar  plexus. 

THE  AUTONOMIC  SYSTEM 

The  chain  of  ganglia  and  nerve  fibers  which  lies  on 
each  side  of  the  vertebral  column  is  usually  called  sym- 
pathetic, because  it  was  formerly  supposed  that  sympa- 
thetic or  reflex  impulses  wrere  carried  by  it.  The  more 
recent  name,  autonomic  is  derived  from  words  meaning 
"a  lawr  unto  itself,"  and  is  appropriate  because  this  sys- 
tem of  nerves  is  entirely  independent  of  the  conscious 
will ;  i.e.,  is  independent  of  that  portion  of  the  brain 
which  consciously  directs.  That  some  of  these  fibers  are 
connected  with  the  brain  through  cranial  nerves  is  ap- 
parent and  all  are  under  the  control  of  some  portion  of 
the  brain ;  but  that  only  means  that  there  are  brain  areas 
over  which  man  exercises  no  control.  Some  of  the  gan- 
glia of  this  system  are  found  in  the  skull  and  are  con- 
nected with  cranial  nerves,  notably  the  ciliary  which 
gives  branches  to  the  iris  or  pupil ;  but  the  larger  num- 
ber lie  along  the  spinal  column  and  are  connected  with 
nearby  spinal  nerves  by  two  roots — a  white  (medul- 
lated)  fiber  which  runs  from  nerve  to  ganglion  and  a 
gray  (nonmedullated)  fiber  which  passes  from  ganglion 
to  nerve  which  afterwards  distributes  it  to  nonstriated 
muscle  fiber.  Through  the  spinal  and  cranial  nerves, 
the  sympathetic  ganglia  are  connected  with  the  central 
nervous  system  in  these  regions  (1)  through  the  third 
nerve  with  the  midbrain,  (2)  through  the  seventh,  ninth, 


120  PHYSIOLOGY   FOR   NURSES 

and  tenth  with  the  medulla,  and  (3)  through  the  spinal 
nerves,  from  the  first  thoracic  to  the  second  lumbar,  with 
the  spinal  cord.  The  branch  connecting  the  spinal  nerve 
and  ganglion  is  called  preganglionic,  while  the  branch 
passing  from  the  ganglion  to  the  muscle  fiber  is  the  post- 
ganglionic.  There  are  three  autonomic  ganglia  in  the 
neck,  but  their  motor  fibers  are  derived  from  the  upper 
thoracic  nerves  and,  after  joining  the  sympathetic  trunk 
in  the  thorax,  ascend  in  it  to  the  cervical  ganglia ;  which, 
however,  give  off  gray  communicating  branches  to  the 
cervical  nerves  which  in  turn  carry  them  to  the  plain 
muscle  fibers  in  the  regions  to  which  they  are  distrib- 
uted. Other  ganglia,  the  collateral  are  found  in  the 
thorax,  abdomen  and  pelvis,  and  still  others,  the  ter- 
minal, in  the  walls  of  the  viscera. 

The  activities  of  this  extensive  nervous  system  are 
directed  to  plain  muscle  fiber  wherever  situated.  The 
muscle  in  the  walls  of  blood  vessels,  however  remote 
from  the  ganglia,  that  in  the  bronchi  and  their  subdi- 
visions, in  the  intestinal  canal,  in  the  iris  and  the  geni- 
tourinary tract,  in  glands  and  other  plain  muscular  or- 
gans throughout  the  body,  all  is  innervated  by  the  auto- 
nomic system. 

Two  opposed  activities  are  characteristic  of  muscular 
fiber  contraction,  by  which  its  ends  are  brought  nearer 
together,  and  relaxation  by  which  the  ends  are  sepa- 
rated. Most  plain  muscle  is  arranged  in  circular  or  lon- 
gitudinal layers  around  some  tubular  body.  Contrac- 
tion of  the  circular  fibers  diminishes  the  size  of  the  tube ; 
relaxation  enlarges  it.  Contraction  of  the  longitudinal 
fibers  shortens  the  tube ;  relaxation  lengthens  it.  Apply 
this  to  a  blood  vessel  and  one  sees  that  contraction  is 
equivalent  to  constriction  and  relaxation  to  dilatation. 

The  best  known  fibers  of  the  sympathetic  are  those 


THE    NERVOUS   SYSTEM  121 

which  excite  constriction  of  blood  vessels,  hence  called 
vasoconstrictor  fibers.  The  less  well  understood  are  the 
relaxers,  hence  called  vasodilator.  The  two  are  vaso- 
motor.  Emotions  may  excite  the  activity-  of  these  nerves. 
The  face  pales  with  fear  and  flushes  with  shame  or  an- 
ger— vasoconstriction  and  vasodilatation.  Exercise  will 
excite  the  dilators,  cold  the  constrictors.  It  is  obvious 
that  this  is  a  form  of  reflex  action,  but  of  reflex  action 
controlled  by  higher  nervous  centers,  neither  under  the 
control  of  the  will  nor  independent  of  the  subconscious 
brain. 

Enlarging-  or  decreasing  the  size  of  the  intestines;  con- 
tracting the  bladder  or  uterus,  changing  the  amount  of 
blood  which  flows  through  the  kidneys,  the  salivary  and 
other  glands,  altering  the  size  of  the  pupil  or  of  the 
bronchioles  are  among  the  many  activities  of  these  widely 
distributed  nerves. 

The  nerve  fibers  derived  from  the  tenth  cranial,  which 
inhibit,  or  slow,  the  heartbeat,  are  carried  to  the  heart 
muscle  through  the  sympathetic  plexus  situated  on  the 
aorta.  They  are  designated  bulbar  autonomic  fibers,  as 
distinguished  from  the  accelerator  fibers  derived  from 
the  upper  thoracic  spinal  nerves  and  joining  the  same 
cardiac  plexus  before  distribution. 

Other  bulbar  autonomic  fibers  are  carried  by  the 
ninth,  seventh,  and  third  nerves.  Those  from  the  latter 
pass  to  the  ciliary  ganglion  and  from  it  to  the  muscle  of 
the  iris  which  regulates  the  amount  of  light  entering 
the  pupil;  or  to  the  ciliary  muscle  which  regulates  ac- 
commodation of  the  eye  for  near  or  distant  vision,  while 
the  similar  fibers  of  the  seventh  and  ninth  probably 
reach  the  tongue,  through  the  chorda  tympani  and  lin- 
gual for  the  anterior  two-thirds  and  the  ninth  for  the 
posterior  third,  and  supply  vasomotor  fibers  to  those  or- 
gans. 


CHAPTER  X 

THE  SPECIAL  SENSES 

We  have  already  seen  that  the  recognition  of  pain, 
pressure,  heat,  and  cold  and  muscular  sensibility  are 
conducted  by  nerve  paths  as  much  specialized  for  their 
purposes  as  is  the  nerve  of  vision;  but  long  habit  has 
applied  the  term  special  senses  to  the  organs  of  taste, 
smell,  vision,  and  hearing. 

TASTE  AND  SMELL 

These  special  senses  are  so  intimately  associated  that 
it  is  difficult  to  make  a  clear  distinction  between  them, 
except  that  the  four  qualities,  sweet,  salt,  sour  and  bit- 
ter or  combinations  of  the  four  are  appreciated  without 
assistance  from  the  olfactory  sense.  Except  these  four, 
all  our  so-called  taste  sensations,  are  really  olfactory 
sensations,  the  nerves  of  smell  being  stimulated  by  the 
substance  eaten  either  before  it  is  placed  in  the  mouth 
or  after  it  has  been  swallowed,  the  odoriferous  particles, 
in  the  latter  case,  entering  the  back  of  the  nose  in  the 
current  of  expired  air  which  follows  the  act  of  swal- 
lowing. 

The  nerves  which  carry  sensations  of  taste  to  the 
brain  are  the  glossopharyngeal  for  the  posterior  one- 
third  of  the  tongue,  fauces  and  palate,  and  the  lingual, 
or  gustatory,  branch  of  the  fifth  for  the  anterior  two- 
thirds  of  the  tongue.  The  taste  fibers-  in  the  gustatory, 
however,  are  derived  from  the  clwrda  tympani  of  the 
seventh.  The  lingual  really  carries  fibers  of  cutaneous 


THE    SPECIAL    SENSES  123 

sensibility  which  endow  the  tongue  with  painful,  tactile, 
or  pressure  and  temperature  sensations.  One's  sense  of 
taste,  then,  is  highly  complex,  being  easily  associated 
with,  or  influenced  by,  temperature,  touch  and  odor. 

The  numerous  papillae  of  the  tongue  are  provided 
with  certain  cells  ending  in  hairlike  projections  which 
are  peripheral  taste  organs.  From  these  the  sense  of 
taste  is  conveyed  along  the  nerve  paths  mentioned  to  a 
point  in  the  temporospJienoidal  lobe,  just  behind  the 
smell  center,  where  the  center  for  taste  is  thought  to  be 
located. 

Because  of  their  number  and  complexity,  it  is  difficult 
to  classify  taste  sensations.  The  bitter,  sweet,  acid  and 
salt  may  be,  and  are,  so  often  mingled  not  only  with 
each  other,  but  with  odors  which  wre  associate  with 
things  tasted  in  the  past  that  we  can  not  separate  the 
various  classes  of  stimulation.  An  apple,  for  instance, 
is  usually  a  combination  of  sweet  and  sour,  but  the 
flavor  so  highly  appreciated  wrould  be  lost  if  the  olfac- 
tory nerves  were  destroyed.  It  is  for  this  reason  that 
food  "loses  its  taste"  when  we  suffer  from  colds,  par- 
ticularly if  both  the  back  and  front  of  the  nose  is 
stopped  by  secretion.  The  distribution  of  the  four  car- 
dinal tastes  is  not  clear,  but  the  back  of  the  tongue  and 
fauces  are  more  sensitive  to  bitter  and  the  front  to 
sweet  stimuli.  There  is  some  evidence  that  there  are 
four  separate  end  organs  and  nerve  fibers  for  the  four 
fundamental  tastes. 

A  substance  which  is  insoluble  can  not  be  tasted.  A 
piece  of  clean  metal  or  glass  stimulates  the  cutaneous 
sensations  when  applied  to  the  tongue,  but  gives  no 
sense  of  taste.  Substances  in  solution,  or  capable  of  be- 
ing rapidly  dissolved  in  the  saliva,  give  rise  to  sensa- 
tions of  taste,  probably  through  a  chemical  reaction  in 


124  PHYSIOLOGY   FOR   NURSES 

which  the  hairlikc  process  is  involved.  Heat  or  cold, 
when  excessive,  interferes  with  the  acuteness  of  taste. 
Smaller  quantities  of  bitter  substances  can  be  tasted 
than  of  any  other,  while  acid,  sweet,  and  salt  each  re- 
quire larger  amounts,  salt  the  largest.  Some  substances 
give  different  sensations  on  different  parts  of  the 
tongue,  as  sulphate  of  soda  which  is  merely  salty  at  the 
tip  of  the  tongue,  but  bitter  at  the  back.  Certain  sub- 
stances dissolved  in  the  blood  give  rise  to  sensations  of 
taste.  The  bile  in  the  blood  in  jaundice  causes  a  bitter 
taste,  while  the  sugar  in  diabetes  causes  a  sweet  tas'.e. 

THE  OLFACTORY  SENSE 

The  course  of  olfactory  sensations  is  from  the  end  or- 
gans of  smell  in  the  roof  and  upper  part  of  the  sides  of 
each  nostril,  along  the  olfactory  nerves  to  the  bulb  and 
thence  to  the  base  of  the  brain  at  the  lower  and  inner 
part  of  the  temporosphenoidal  lobe  just  in  front  of  the 
center  for  taste. 

The  smell  sense  is  one  of  the  oldest  in  the  history  of 
life.  When  highly  developed  it  was  not  only  of  great 
defensive  strength  in  enabling  its  possessor  to  detect 
the  presence  of  enemies,  but  was  of  equal  offensive  serv- 
ice in  the  pursuit  of  prey.  In  man  it  has  dwindled  to 
such  an  extent  that  he  vaguely  defines  odors  as  pleas- 
ant or  disagreeable,  while  a  dog  can  still  detect  the 
odor,  of  a  man,  imperceptible  usually  to  himself  and  as- 
sociates, and  follow  him  unerringly  after  hours  have 
elapsed  and  pick  him  out  of  a  crowd  of  others. 

The  substances  which  arouse,  or  stimulate,  the  sense 
of  smell,  give  off  inappreciable  particles,  probably  gas- 
eous in  form,  which  are  carried  by  inhaled  air  to  the 
end  organs  of  the  olfactory  nerve,  are  there  dissolved 
by  the  moisture  present  and  chemically  stimulate  the 


THE    SPECIAL   SENSES  125 

hair  processes.  Many  odors,  like  those  of  fruits,  wines, 
and  many  foods  are  habitually  confounded  with  the 
sense  of  taste.  Some  disagreeable,  or  foul  odors  are 
simply  associated  in  our  memories  with  disagreeable  im- 
pressions and  may  be  agreeable  to  other  persons.  The 
garlic  or  onion  odor  and  that  of  musk,  excite  pleasur- 
able sensations  in  some  and  only  disagreeable  sensation 
in  others.  These  effects  are  probably  memories  and  not 
differences  in  the  character  of  the  chemical  reaction  in 
different  individuals.  The  olfactory  nerves  are  easily 
fatigued,  when  stimulated  for  too  long  a  period,  or  with 
too  much  of  the  odor.  The  amount  of  gaseous  material 
which  can  be  detected  is  innnitesimally  small.  Camphor 
can  be  detected  when  only  one  part  is  present  in  four 
hundred  thousand,  vanillin  (the  active  principle  of 
vanilla),  one  part  in  ten  million,  while  other  substances 
can  l)e  detected  in  amounts  still  more  minute. 

VISION 

Essentially  the  organ  of  vision  is  an  apparatus  by 
which  an  image  of  objects  may  be  thrown  on  a  mirror, 
composed  of  nerve  terminals  sensitive  to  light,  the  sen- 
sation, or  impulse,  thus  produced  being  conducted  along 
paths  of  nerve  tissue  to  the  gray  matter  covering  a  cer- 
tain area  of  the  brain.  The  particular  region  of  the 
brain  is  the  cuneate  portion  of  the  occipital  lobe,  and 
the  path  of  conduction  is  by  the  optic  tracts,  chiasm  and 
nerves  from  the  retina,  the  concave  nervous  mirror  in 
which  the  object  is  reflected.  We  actually  see  with  the 
brain,  just  as  we  feel  with  the  brain.  If  the  cuneate 
area  be  destroyed  we  are  blind  no  matter  how  perfect 
the  remainder  of  the  seeing  apparatus  may  be. 

Bays  of  light  are  vibrations  of  the  ether  which  sur- 
rounds us,  differing  in  length  and  rapidity  for  different 


•    -                     3 

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It 

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V 

L,    ru   w 

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\  S  <i  -^ 

i 

C- 

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il 

THE    SPECIAL   SENSES 


127 


colors.  The  slowest  vibrations  are  red.  The  most  rapid 
violet.  A  mixture  of  all  the  colors  of  the  spectrum  makes 
white  light,  or  light  without  color,  a  result  of  the  min- 
gling of  the  various  rates  of  vibration  of  the  different 
colors.  In  order  that  the  eye  may  serve  its  purpose  with- 
out constantly  turning  the  head,  the  eyeball  is  provided 
with  ocular  muscles  which  can  move  the  ball  in  all  direc- 
tions; and,  that  the  amount  of  light  may  be  neither  too 


Fig.  29. — Section  through  the  anterior  portion  of  the  eye:  C,  the  cornea; 
I,  the  iris  (note  the  circular  muscular  fibers  cut  across  at  the  margin)  ;  L, 
the  lens;  Ci,  the  ciliary  process;  S,  the  suspensory  ligament;  Scl,  the  scle- 
rotic or  outer  protective  coat  of  the  eye.  (From  a  preparation  by  P.  M.  Spur- 
ney.)  (Pearce-Macleod,  Fundamentals  of  Human  Physiology.) 

great  nor  too  little,  provision  must  be  made  for  regulat- 
ing the  size  of  the  opening  through  which  light  is  admit- 
ted to  the  interior  of  the  eyeball.  This  is  accomplished 
by  putting  a  curtain,  with  a  hole  in  the  middle,  in  the 
fore  part  of  the  eyeball,  and  providing  it  with  muscular 
fibers  which  can  increase  or  dimmish  the  size  of  the  hole. 


128  PHYSIOLOGY   FOR   NURSES 

Light,  however,  does  not  travel  in  a  straight  line  when 
it  passes  from  a  medium  of  one  density  to  that  of  a 
greater  density.  If  one  places  a  straight  stick  in  a  glass 
of  water,  no  matter  how  clear,  the  stick  appears  to  be 
bent.  This  bending  of  the  light  rays  is  called  refraction. 
When  light  passes  into  the  eyeball,  it  is  leaving  a  me- 
dium of  little  density — the  air — and  passing  through  sub- 
stances of  greater  density, — the  structures  in  the  eye- 
ball in  front  of  the  retina. 

If  light  is  transmitted  through  a  doubly  convex,  trans- 
parent body,  the  rays  will  be  bent  in  such  a  way  that 
behind  the  body  they  will  all  come  together  at  one 
point.  This  is  focusing  the  rays.  The  rays  of  light 
travel  on  lines  parallel  with  one  another;  and  are  prac- 
tically all  parallel  when  emitted  from  objects  at  a  dis- 
tance of  twenty  feet.  If  the  lens,  the  convex  transpar- 
ent body,  be  of  uniform  curvature  on  both  surfaces,  the 
ray  which  passes  through  the  exact  center  will  be  per- 
fectly straight ;  but  those  which  enter  above  will  be  bent 
down,  those  from  below,  up ;  and  those  from  each  side, 
towards  the  central  ray.  Hence  they  will  all  be  thrown 
on  the  intercepting  surface  as  a  cone  whose  apex  is  the 
point  behind  the  lens  corresponding  to  the  bending  or 
refracting  power  of  that  lens,  and  whose  base  will  be 
the  back  of  the  lens.  If,  however,  the  object  from  which 
the  light  is  reflected  be  too  near  the  front  of  the  lens, 
the  rays  are  not  parallel,  will  not  strike  the  lens  at  the 
same  angle,  and  will  be  unequally  bent  and  throw  a 
blurred  and  indistinct  image  on  the  intercepting  sur- 
face. The  distance  between  the  lens  and  receiving  sur- 
face at  which  the  point  of  the  light  cone  is  intercepted 
is  the  main  focus.  The  distance  between  the  front  of 
the  lens  and  the  illuminated  object  at  which  the  rays 
from  that  object  enter  the  lens  as  parallel  rays  is  the 


THE   SPECIAL   SENSES 


129 


near  point;  i.e.,  the  nearest  point  to  the  eye  at  which 
that  object  can  be  distinctly  seen.  Nearer  than  this  the 
object  is  blurred.  If  the  convexity  of  the  lens  be  in- 
creased, if  it  becomes  more  nearly  a  perfect  sphere,  the 
bending  of  the  rays  will  be  increased  equally  and  the 
focal  point  will  be  closer  to  the  back  of  the  lens.  Con- 
versely, flattening  the  lens  would  diminish  the  refrac- 
tion and  the  focus  would  be  at  a  more  distant  point  be- 
hind the  lens.  In  order  to  see  clearly,  therefore,  the  eye 
must  have  the  power  of  accommodating  itself  to  the  dis- 
tance of  the  objects,  since  the  power  of  seeing  at  a  fixed 


Fig.    30. — Formation   of   image   on   retina.      O.A.    is  the   optic   axis.      (Pearce- 
Macleod,  Fundamentals  of  Human  Physiology.) 

distance  only  would  be  of  very  little  use.  This  purpose 
might  be  accomplished  either  by  moving  the  lens  back- 
wards and  forwards  or  by  flattening  or  bulging  of  the 
lens.  In  some  fishes  the  former  method  is  observed,  but 
in  mammals  the  latter  is  the  uniform  rule.  This  action 
of  the  eye  is  called  accommodation  and  is  carried  out  by 
a  muscular  arrangement  to  be  explained. 

Inverted  Imag-es, — When  an  image  is  thrown  through 
a  small  opening,  on  a  deeply  concave  mirror,  the  rays 
from  the  top  of  the  object  reflected  strike  on  the  lower 
and  those  from  the  bottom  on  the  upper  part  of  the 
concavity.  Hence  the  image  is  inverted.  All  objects 


130  PHYSIOLOGY   FOR   NURSES 

reflected  by  or  impressed  on  the  retina  arc  thus  in- 
verted, but  our  brains  have  become  so  accustomed  to 
reverse  them  that  we  are  never  even  aware  of  the  fact. 
It  is  conceivable  that  there  could  be  such  a  disturbance 
of  mental  processes  as  to  change  this  automatic  mental 
action  and  make  us  see  everything  upside  down. 

The  eyeball  consists  of  an  outside,  middle,  and  inner 
coat.  The  outer  coat  is  mainly  protective,  except  for 
its  anterior  fifth,  the  cornea,  which  transmits  and  re- 
fracts light.  The  middle  coat  is  vascular  and  the  inner 
coat  is  the  active  part  responding  to  light  as  a  stimulus. 

The  cornea  is  placed  in  front  of  the  iris  and  lens  and 
behind  the  lens  is  the  vitreous  humor  which  is  separated 
from  the  retina  by  a  very  delicate  membrane.  The 
cornea  and  the  lens  are  the  chief  refracting  media.  The 
iris  is  the  perforated  curtain  which  regulates  the 
amount  of  light. 

The  iris,  the  colored  portion  of  the  eye,  has  circular 
muscular  fibers  which  surround  the  pupil  and  can,  by 
contracting,  decrease  its  size.  There  are  also  radiating 
fibers  which  can  widen  or  dilate  the  pupil.  If  either 
should  stick  to  the  lens,  in  front  of  which  they  lie,  the 
pupil  would  be  contracted  or  dilated  unequally  and 
appear  as  a  jagged  instead  of  a  circular  opening. 

The  lens,  crystalline  lens,  is  surrounded  by  an  elastic 
membrane  called  its  capsule.  This  membrane  is  con- 
nected with  a  muscle,  the  ciliary,  which  is  in  turn  fas- 
tened to  the  middle  or  choroid  coat.  In  the  normal 
condition,  where  the  eyes  are  used  to  view  distant  ob- 
jects, the  ciliary  muscle  is  at  rest  and  the  elastic  capsule 
flattens  the  lens  without  fatigue  to  itself;  but  when  the 
eye  must  accommodate  itself  for  near  vision,  the  muscle 
contracts,  draws  the  choroid  forward,  relaxing  the 
capsule  while  the  lens,  by  its  own  elasticity,  becomes 


THE    SPECIAL   SENSES  131 

more  convex,  mainly  by  bulging  forward,  since  it  meets 
with  less  resistance  in  that  direction.  This  is  the  power 
of  accommodation  for  near  vision  and  varies  greatly  in 
its  range  in  different  people  and  at  different  ages.  The 
near  point  is  closest  to  the  eye  in  youth  and  increases 
rapidly  with  age.  At  ten  it  is  less  than  three  inches, 
while  at  sixty  it  is  more  than  a  yard — a  distance  at 
which  moderate  print  can  not  be  read.  There  is1  prac- 
tically no  far  point.  Distant  objects  are  visible  in  pro- 
portion to  their  size.  But  the  nearest  point  at  which 
the  rays  of  light  are  parallel  may  be  called  the  distant 
point. 

A  normal  eye  is  called  emmetropic.  An  abnormal  eye, 
not  one  affected  by  acute  disease,  may  be  myopic,  hyper- 
metropic  or  presbyopic. 

It  has  been  stated  that  if  the  lens  is  too  convex 
1he  focal  point  will  fall  closer  to  the  lens.  The  rays 
would  then  form  a  cone  and,  if  they  are  not  intercepted, 
disperse  again  forming  a  second  cone  whose  apex  would 
begin  at  the  apex  of  the  first  cone.  This  would  result 
in  diverging  rays  striking  on  the  retina  and  an  indis- 
tinct image.  The  same  result  would  follow  if  the  retina 
were  too  far  from  the  lens,  i.e.,  if  the  eye  were  too  long. 
This  is  actually  the  case  in  the  myopic  or  near-sighted 
eye.  The  latter  name  indicates  that,  to  get  a  clear 
image,  the  object  must  be  brought  nearer  the  eye  so 
that  divergent  instead  of  parallel,  rays  may  be  thrown 
on  the  lens.  Glasses  which  break  up  the  parallel  into 
diverging  rays  would,  therefore,  correct  this  defect. 
Children  are  not  usually  born  myopic  but  have,  or 
acquire,  perhaps  more  frequently  the  latter,  weakness 
of  the  coats  of  the  eyeball  which  give  way  under  the 
strain  of  reading  by  bad  light  or  in  improper  positions 
and  the  eye  becomes  too  long. 


132 


PHYSIOLOGY    FOR    NURSKS 


Hypermetropic,  or  far-sighted,  eyes  have  just  the 
opposite  defect.  The  eye  is  too  short  for  the  convexity 
of  the  lens  and  the  cone  is  intercepted  by  the  retina 


Fig.  31. — Errors  in  refraction:  E  shows  the  formation  of  the  image  on 
the  retina  in  the  normal  or  emmetropic  eye;  //  shows  the  condition  in  long- 
sight,  or  hypermetropia,  where  the  eyeball  is  too  short;  M  shows  the  condi- 
tion in  short-sight,,  or  myopia,  where  the  eyeball  is  too  long.  (Pearce-Macleod, 
Fundamentals  of  Human  Physiology.) 

before  its  apex  is  reached.  The  same  blurring  occurs 
as  in  the  myopic  eye  but  for  the  opposite  reason.  Hence 
glasses  which  converge  the  rays  are  here  necessary. 
This  condition  is  usually  congenital. 


THE    SPECIAL    SENSES  133 

Presbyopia  is  old-sightedness.  Here  the  lens  has  be- 
come so  hard  that  the  power  of  accommodation  is  lost. 
It  usually  begins  between  the  fortieth  and  fiftieth  years. 
Distant  vision  remains  good,  but  the  power  of  accommo- 
dation for  near  vision  is  lost. 

If  the  surfaces  of  the  cornea  and  lens  be  not  segments 
of  a  true  sphere,  there  is  another  error  of  refraction 
called  astigmatism  or  inability  to  see  a  point.  It  is 
often  combined  with  the  near-  or  far-sighted  defect. 

The  muscles  which  move  the  eye  ball  are  supplied  by 
the  third,  fourth  and  sixth  cranial  nerves.  The  fibers  of 
the  ciliary  muscle  and  iris,  nonstriated,  are.  supplied  by 
the  ciliary  ganglion  of  the  sympathetic  .system,  which 
receives  motor  fibers  from  the  third  and  sensory  from 
the  fifth.  There  are  constrictor  and  dilator  fibers  for 
the  pupil,  constrictors  being  stimulated  by  strong  light 
and  dilators  by  weak. 

HEARING 

The  organ  of  hearing  is  of  such  minute  and  complex 
anatomic  formation  that  only  an  outline  will  be  given. 

A  very  simple,  diagrammatic,  conception  is  that  of  a 
membrane  which  vibrates  as  the  result  of  blows  struck 
by  air  waves,  the  membrane  being  attached  to  levers 
which  create  waves  in  a  fluid  which  is  in  contact  with 
the  terminals  of  the  auditory  nerve  which  conveys  the 
stimulus  to  a  definite  area  of  the  brain.  A  tense  mem- 
brane vibrates  at  a  given  rate  only,  and  responds  to 
high  or  low  rates  of  vibration  as  the  membrane  is 
stretched  or  relaxed.  A  drum  is  essentially  a  mem- 
brane stretched  across  a  circle,  and  such  a  membrane, 
when  struck,  causes  air  waves  or  vibrations  at  a  given 
number  each  second;  but  if  the  membrane  be  stretched 
at  one  part  and  relaxed  at  another,  it  will  practically 


134 


PHYSIOLOGY   FOR   NURSES 


act  as  two  (Iriiius,  the  lonscr  segment  vibrating  more, 
and  the  relaxed  less,  rapidly.  At  the  bottom  of  our 
ears  we  have  a  membrane  (tympanic)  familiarly  known 
as  the  "ear-drum"  which  can  be  relaxed  or  stretched 
to  respond  to  blows  of  different  character.  The  nerve 
terminals  themselves  are  arranged  to  respond  to  waves 


Fig.  32. — Tympanum  of  right  side  with  the  auditory  ossicles  in  place  (  Mor- 
ris) :  I,  incus  (like  bicuspid  tooth)  with  one  process  (_.?)  attached  to  wall  of 
tympanum  and  the  other  running  downwards  to  articulate  at  9  and  8,  the 
stapes;  10,  head  of  malleus  attached  to  tympanic  membrane.  (From  llowell's 
Physiology.) 

of  different  lengths;  i.e.,  vibrations  which  may  be  as 
many  as  four  thousand  or  as  few  as  thirty  to  the  second. 
In  man  the  external  ear  is  of  little  use  in  gathering- 
sound  and  concentrating  it  upon  the  drum,  though  it 
seems  to  serve  its  purpose  much  better  in  many  lower 
animals.  The  tympanic  membrane  closes  the  auditory 


THE    SPECIAL    SENSES  135 

canal  and  is  in  contact  with  the  air  on  both  sides — on 
the  outer  side  with  the  atmosphere  and  on  the  inner 
with  the  inspired  air  as  it  reaches  the  back  of  the  nose. 
This  arrangement  secures  equal  pressure  on  the  two 
faces  of  the  membrane  and  its  importance  is  readily 
seen  in  the  impaired  sense  of  hearing  when  the  nose  is 
blocked  up  by  a  cold  "in  the  head."  Attached  to  the 
inner  face  of  this  drum  and  stretching  across  the  middle 
ear  (tympanic  cavity)  is  a  chain  of  minute  bones  (audi- 
tory ossicles)  so  arranged  that  they  act  as  a  bent  lever 
which  moves  with  every  vibration  of  the  drum  and  con- 
veys these  waves  to  a  second  drum  which  closes  an 
opening  by  which  the  middle  would  otherwise  com- 
municate with  the  inner  ear.  The  latter  is  the  part  in 
which  the  nerve  terminals  are  located.  Briefly  de- 
scribed the  organ  consists  of  a  basement  membrane 
stretched  from  the  flanges  of  a  screwlike  center  to  the 
surrounding  Avail,  on  which  rest  the  ends  of  nerve  cells 
which  terminate  in  hairlike  processes  in  contact  with 
which  is  a  very  delicate  membrane  which  is  moved  by 
the  waves  created  in  the  fluid  (endolymph)  which  bathes 
the  organ.  The  movements  of  the  overlying  membrane 
are  communicated  to  the  hairs  and  these  in  turn  stimu- 
late the  nerve  cells  and  the  impulse  or  sensation  is  con- 
veyed to  the  brain. 

Not  all  sound  is  conveyed  through  the  external  ear. 
The  sound  of  our  own  voices  is,  in  part  at  least,  con- 
veyed through  the  bones  of  the  head.  A  tuning  fork 
placed  on  the  teeth  will  be  heard  so  long  as  its  vibra- 
tions can  excite  movements  of  the  ossicles.  A  simpler 
experiment  is  to  stop  the  ears  and  apply  the  teeth  to  a 
watch,  whose  ticking  can  be  heard  plainly  through  the 
teeth. 

The  auditory,  or  eighth  nerve  is  not  entirely  given 


136  PHYSIOLOGY   FOR    XTKSKS 

over  to  conveying  sound  waves.  A  part  of  this  nerve 
is  distributed  to  the  semicircular  canals  and,  apparently, 
conducts  sensation  to  that  part  of  the  cerebellum  which 
aids  in  maintaining  equilibrium.  They  are  not  the  only 
nerve  fibers  which  convey  impulses  necessary  for  this 
function,  but  are  important  paths  for  such  stimuli. 
The  auditory  canal,  which  is  nearly  an  inch  in  length, 


Fig.  33. — Semidiagrammatic  section  through  the  right  ear  (Czermak);  G, 
external  auditory  meatus;  T,  membrana  tympani;  P,  tympanic  cavity  or 
middle  ear  with  the  auditory  ossicles  stretching  across  it  and  the  Kustachian 
tube  (J3)  entering  it;  o,  oval  window;  r,  round  window;  B,  semicircular 
canals;  5",  cochlea;  Vt,  upper  canal  of  cochlea;  Pt,  lower  canal  of  cochlea. 
(From  llowell's  Physiology.) 

is  the  site  of  the  accumulation  of  that  mixture  of  the 
secretion  of  the  sebaceous  glands  with  worn-out  cells 
which  we  call  "ear  wax."  It  is  often  present  in  amounts 
sufficient  to  impair  acuteness  of  hearing  and  must  IK- 
softened  and  removed,  a  duty  frequently  falling  upon 
the  nurse. 

That  our  sense  of  the  location  and  distance  from  which 
sounds  come  is  not  very  acute,  is  a  matter  of  common 


Fig.  34. — Diagrammatic  view  of  the  organ  of  Corti  (Testut) :  D,  basilar 
membrane;  A,  B,  inner  and  outer  rods  of  Corti;  6,  6',  6",  hair  cells;  7,  f  t 
supporting  cells.  (From  Howell's  Physiology.) 


THE   SPECIAL  SENSES  137 

observation.  When  we  wish  to  locate  a  sound  we  in- 
stinctively call  in  the  aid  of  other  senses,  the  eye  no- 
tably, and  look  about  us  to  see  if  vision  can  accurately 
place  what  hearing  only  suggests.  It  is  said  that  the 
location  of  sound  is  more  definite  when  both  ears  are 
employed. 


CHAPTER  XI 

SLEEP 

Sleep  is  not  only  necessary  to  rest  a  tired  mind  and 
body,  but  more  essential  to  life  than  food  itself.  Com- 
plete fasting  has  extended  over  periods  measured  by 
weeks,  but  total  absence  of  sleep  for  four  or  five  days 
is  likely  to  end  fatally.  The  imperative  nature  of  the 
demand  for  sleep  is  shown  in  the  thousands  of  cases  in 
which  soldiers  have  slept  on  horseback,  while  marching 
and  even  when  on  sentry  duty,  when  the  penalty  is 
death.  Notwithstanding  the  universality  of  this  phys- 
iologic function,  we  are  almost  entirely  in  the  dark  as 
to  its  mechanism,  a  fact  sufficiently  proved  by  the 
number  of  theories  advanced  and  the  contradictory 
nature  of  the  evidence  adduced  in  their  support.  Some 
of  the  changes  which  occur  during  sleep  are  established 
and  may  be  accepted  as  proved. 

Not  only  is  night,  when  many  forms  of  work  must 
cease  for  want  of  light,  the  time  during  which  most 
people  sleep,  but  there  seems  little  reason  to  doubt  the 
statement  that  night  sleep  is  more  restful  than  that 
during  daylight.  "Daylight  sleep,  in  fact,  is  less  re- 
cuperative and  less  profound  and  unbroken  than  night 
sleep."  (Luciani).  Sleep  is  usually  preceded  by  drowsi- 
ness, indicated  by  a  pricking  sensation  in  the  eyes, 
drooping  of  the  upper  lid,  probably  from  fatigue  of  the 
muscle  which  supports  it,  dulling  of  the  mind  ana  in- 
ability to  fix  the  attention.  Usually  we  compose  our- 
selves, the  drowsiness  deepens  until  we  lose  all  idea  of 

138 


SLEEP  139 

our  surroundings  and  deep  sleep  succeeds,  to  be  fol- 
lowed by  a  lighter  slumber  until  this  in  turn  gives  way 
to  a  condition  quite  similar  to  drowsiness,  a  half  con- 
sciousness of  our  surroundings,  an  arousing  of  atten- 
tion until  we  are  completely  conscious  or  "awake." 
Sleep,  in  healthy  adults,  usually  lasts  from  seven  to 
eight  hours,  though  the  time  given  or  required  varies 
greatly  with  the  individual  and  with  age.  Newborn 
infants  sleep  from  eighteen  to  twenty  hours  a  day,  old 
people  five  or  six.  In  other  words  when  growth  is  most 
active,  sleep  is  most  needed.  In  the  old  there  is  no 
growth  and  comparatively  little  repair,  while,  during 
the  active  period  of  life,  though  growth  has  stopped, 
repair  is  steady  and  imperative. 

The  depth  of  sleep  varies  greatly.  Normally  it  would 
seem  that  the  first  two  hours  are  characterized  by  the 
deepest  sleep,  which  gives  way  to  a  lighter  type  which, 
in  its  turn,  is  succeeded  by  more  profound  unconscious- 
ness a  short  time  before  waking.  Nearly  all  secretions 
are  diminished  during  sleep.  The  tears,  which  moisten 
the  eyeballs  and  lids,  are  nearly  absent  even  in  drowsi- 
ness, the  dryness  of  the  mouth  and  throat  on  waking 
are  evidence  of  the  lack  of  salivary  secretion,  while  the 
high  color  and  comparatively  small  amount  of  urine 
accumulated  during  the  night,  show  that  at  least  the 
watery  part  of  the  urine  is  decreased.  On  the  contrary 
perspiration  increases  to  such  an  extent  that  it  has  been 
asserted  that  as  much  is  produced  during  seven  sleeping 
as  in  fourteen  waking  hours.  Respiration  is  slower  in 
sleep  and  often  becomes  intermittent,  particularly  in 
children  and  the  old,  and  the  costal  type  of  breathing 
is  the  rule.  The  heart  beats  more  slowly,  though  it  is 
said  to  increase  in  rapidity  near  the  waking  hour.  Su- 
perficial blood  vessels  are  dilated  and  congested,  while 


140  PHYSIOLOGY  FOR   NURSES 

there  is  an  appreciable  fall  in  body  temperature,  the 
lowest  occuring  between  midnight  and  three  in  the 
morning. 

Not  all  of  our  senses  fall  asleep  at  the  same  time  or 
to  the  same  degree.  Light  is  first  lost,  in  fact  we  de- 
liberately cut  off  the  light  by  closing  the  lids.  Hearing 
is  never  so  completely  abolished  and  sensitiveness  to 
touch  is  present  in  all  but  the  most  profound  slumber. 
Taste  and  the  sense  of  smell  are  almost  completely 
abolished.  It  seems  that  loss  of  sensibility  of  all  kinds 
is  due  to  a  change  in  the  cortex  of  the  brain  and  not  in 
either  the  peripheral  nerve  terminals  or  in  the  conduct- 
ing paths.  While  our  muscles  are  relaxed,  they  will 
carry  out  coordinated  movements  without  our  being 
conscious  either  of  the  stimulus,  like  tickling  the  nose  or 
lids,  or  of  the  movement  to  brush  away  the  offending 
body.  Of  course,  frequent  repetition  of  the  stimulus 
will  awaken  one.  Sleep,  however,  while  mainly  affect- 
ing the  brain,  is  not  confined  to  it.  All  of  our  tissues 
and  organs  sleep. 

There  are  many  theories  of  sleep  but  the  chief  ones 
are  chemical  or  circulatory. 

A  chemical  theory  supposes  that  the  body  forms,  dur- 
ing waking  hours,  substances  of  a  more  or  less  poison- 
ous character  which,  when  accumulated  in  sufficient 
quantity  prevent  (inhibit)  the  activity  of  the  cortex; 
or  that  an  increase  in  the  acid  waste  products  of  the 
body  will  exercise  the  same  influence. 

A  circulatory  theory  explains  the  periodic  occur- 
rence of  sleep  by  assuming  that  there  is  an  absence  of 
sufficient  blood  in  the  brain  (anemia)  to  keep  up  its 
normal  activity,  and  that  sleep  follows,  basing  the 
theory  largely  on  the  well-established  fact  that  experi- 
mental interference  with  the  blood  supply  of  the  brain 


SLEEP  141 

will  produce  unconsciousness.  The  theory  supposes  that 
the  vasomotor  center  in  the  medulla  becomes  fatigued 
during  the  day's  work,  allows  the  vessels  in  other  parts 
of  the  body  to  dilate  and  hold  more  blood  and  auto- 
matically decreases  the  amount  flowing  through  the 
brain.  No  theory  has  met  all  the  objections.  We  can, 
in  effect,  say  nothing  confidently  save  that  sleep  is  nec- 
essary, that  it  follows  bodily  more  than  mental  activity 
and  that  some  conditions,  notably  mental  worry,  may 
produce  a  condition  (insomnia)  most  trying  to  patient, 
physician,  and  nurse,  and  sometimes  beyond  the  power 
of  drugs. 

Dreams  are  attendants  of  sleeping  hours  which  have 
not  been  satisfactorily  explained.  They  at  least  serve 
to  show  that  all  of  the  brain  is  not  asleep,  or  not  pro- 
foundly asleep ;  but  whether  we  dream  during  the  en- 
tire sleeping  period  and  remember  only  those  dreams 
which  immediately  precede  waking,  or  whether  we 
dream  only  when  in  the  light,  or  disappearing,  sleep 
which  precedes  returning  consciousness,  is  a  matter 
entirely  unsettled. 

Hypnotic  sleep  should  be  mentioned,  but  not  dis- 
cussed. Many  observers  doubt  its  occurrence  while 
those  who  believe  in  its  existence  can  furnish  no  satis- 
factory explanation  of  the  phenomenon. 

The  sleep  induced  by  drugs  should  be  alluded  to.  It 
is  neither  so  restful  nor  so  recuperative  as  normal  sleep, 
though  it  may  be  much  more  profound.  The  type  of 
drug-induced  sleep  will  vary  with  the  hypnotic  em- 
ployed and  with  the  dose,  as  well  as  with  the  suscepti- 
bility of  the  patient  and  his  drug  habits  and  ante- 
cedents. 


CHAPTER  XII 

REPRODUCTION 

The  organs  concerned  in  reproduction  are,  in  the 
female,  the  ovary  Avhich  produces  the  egg  or  cell  from 
which  the  new  being  is  to  be  formed,  the  fallopian  tube, 
which  conveys  the  egg  to  the  uterus,  which  is  the  hatch- 
ing apparatus,  and  the  vagina  through  which  the  egg 
is  fertilized  and  the  child  born. 

Menstruation  is  seen  in  the  female  only.  It  begins 
usually  in  the  fourteenth  or  fifteenth  year  and  recurs 
at  intervals  of  about  28  days  until  the  "change  of  life," 
climacteric,  or  menopause,  which  occurs  between  the 
forty-fifth  and  fiftieth  years.  The  appearance  of  the 
menstrual  flow  is  earlier  in  warm  than  in  cold  climates; 
and  the  cessation  of  the  function  varies  greatly  in  dif- 
ferent individuals.  Removal  of  the  ovaries  causes  an 
artificial  menopause.  It  is  clear,  then,  that  the  activity 
of  the  ovary  is  periodic  and  is  responsible  for  menstru- 
ation; but  the  actual  flow  of  blood  is  a  function  of  the 
uterus,  probably  in  preparation  for  the  reception  of  the 
fertile  egg.  The  lining  (mucous)  membrane  of  the 
uterus  thickens  and  becomes  engorged  with  blood  four 
or  five  days  before  the  appearance  of  the  flow.  There 
follows  a  period,  usually  of  four  days,  in  which  there  is 
hemorrhage  into  the  uterus  and  the  swollen  membrane 
is  cast  off  and  this  is  followed  by  about  a  week  of  re- 
generation during  which  time  the  membrane  returns  to 
its  normal  condition.  The  next  twelve  days  constitute 
the  resting  period. 

142 


REPRODUCTION  143 

In  perfectly  healthy  women  the  other  body  func- 
tions are  scarcely  affected  by  the  recurrence  of  the 
menstrual  period.  There  is  usually  some  slight  lack  of 
well  being  and  the  woman's  efficiency  is  not  quite  up 
to  the  normal  standard.  Any  further  symptoms  must 
be  referred  not  to  menstruation  but  to  some  diseased 
condition  affecting  either  the  generative  or  some  ad- 
jacent viscera. 

The  ovum  (egg)  is  probably  carried  into  the  fallopian 
tube  by  the  cilia  on  its  extremity,  and  meets  the  male 
cell  (spermatazoon)  shortly  after  the  entrance  of  the 
ovum  into  that  tube.  Usually  the  now  fertilized  ovum 
is  swept  into  the  uterine  cavity  and  becomes  attached 
to  the  wall  of  the  uterus  where  the  placenta  is  formed 
and  remains  until  the  termination  of  pregnancy;  but, 
owing  to  unknown  causes,  the  impregnated  ovum  is 
sometimes  arrested  in  the  tube  and  an  effort  is  made  to 
produce  the  fetus  in  that  narrow  passage.  This  is  a-  tubal 
pregnancy,  whose  natural  history  ends  in  rupture  of 
the  tube  and  the  death  of  the  mother,  unless  the  con- 
dition is  discovered  and  relieved  by  surgical  interfer- 
ence. In  rare  cases  the  ovum  is  impregnated  in  the 
peritoneal  cavity,  never  entering  the  tube,  constituting 
a  true  abdominal  pregnancy. 

The  placenta  is  the  organ  which  conveys  air  and  nour- 
ishment to  the  fetus  during  uterine  life.  The  fetus  is 
never  in  contact  with  the  mother's  blood,  and,  though 
its  OAvn  heart  beats,  is  dependent  upon  the  maternal 
heart  to  drive  blood  containing  both  food  and  oxygen 
into  the  placenta  from  which  it  is  carried  into  the  fetal 
vessels.  Between  the  fetus  and  the  mother's  blood  are 
interposed  tissues  which  permit  diffusion  through  them 
in  a  way  similar  to  that  by  which  the  mother's  own 
tissues  are  nourished  by  her  blood  stream,  In  other 


144  PHYSIOLOGY  FOR   NURSES 

words  the  fetus  is,  practically,  a  part  of  the  mother's 
body. 

Parturition  is  the  act  of  bringing  the  child  into  the 
world.  The  "term  of  pregnancy"  is  about  ten  lunar 
months  (280  days)  from  the  time  of  the  last  menstrua- 
tion. Delivery  is  accomplished  by  involuntary  contrac- 
tion of  the  uterine  muscle  fiber  aided  by  voluntary  con- 
traction of  the  diaphragm  and  the  muscles  of  the 
abdominal  wall.  The  cause  of  the  uterine  contractions 
is  unknown,  though  possibly  a  hormone  produced  by 
the  mammary  gland  may  excite  them. 

The  mammary  gland  begins  to  enlarge  and  form 
secreting  alveoli  shortly  after  pregnancy  is  established 
and  towards  the  end  secretes  a  small  amount  of  a  fluid 
called  colostrum.  After  delivery  the  gland  is  actively 
stimulated  and  rapidly  enlarges.  For  a  few  days  the 
secretion  retains  the  character  of  colostrum,  but,  usually 
on  the  third  or  fourth  day,  the  flow  of  milk  has  become 
well  established. 

There  is  some  evidence  that  the  fetus  forms  a  hormone 
which  stimulates  growth  of  the  mammary  gland,  but 
inhibits  its  secretion.  This  substance  is  withdrawn  when 
the  fetus  is  born  and  its  removal  permits  the  functional 
activity  of  the  gland. 

That  the  mammary  gland  is  under  the  control  of  the 
central  nervous  system  is  indicated  by  the  effects  of 
various  emotions  upon  its  secretion;  but  there  are  no 
known  secretory  nerves,  though  there  are  vasoconstric- 
tor and  vasodilator  fibers  as  in  the  other  glands. 

The  male  cell  which  fertilizes  the  ovum  is  secreted  by 
the  testicle,  an  organ  analogous  to  the  ovary  of  the 
female. 


CHAPTER  XIII 

GROWTH  AND   OLD  AGE 

The  rate  of  growth  does  not  increase  from  birth  to 
maturity  and  then  decline,  but  declines  steadily  from 
the  impregnation  of  the  ovum  until  death.  The  fetus 
grows  most  rapidly  during  the  first  month  of  uterine 
life — the  rate  of  growth  declining  from  this  time  until 
the  end — the  average  child  nearly  triples  its  weight  at 
birth  in  its  first  year,  but  only  gains  about  twenty-five 
per  cent  during  the  second  year,  and  at  a  still  lower 
rate  for  each  succeeding  year.  Other  changes  indicate 
the  gradual  loss  of  the  power  of  living  always — bones 
become  more  brittle,  cartilage  more  rigid,  muscles  less 
elastic,  all  changes  which,  while  serving  a  useful  pur- 
pose in  some  cases,  none  the  less  show  that  animals  be- 
gin to  die  before  they  are  born,  and  that,  independent 
of  disease,  death  is  as  natural  a  process  as  birth.  As 
few,  however,  die  a  natural  death,  a  death  which  is 
simply  the  wearing  out  of  the  protoplasm  of  which  the 
body  is  made,  we  have  little  or  no  idea  of  the  number 
of  years  which  a  perfectly  healthy  person  might  live  if 
no  disease  or  accident  intervened  to  bring  life  to  a  sud- 
den termination.  The  only  authentic  case  of  great  lon- 
gevity is  that  of  Thomas  Parr  (usually  known  as  "old 
Parr")  who  reached  the  age  of  one  hundred  and  fifty-two 
years,  and  is  supposed  to  have  been  brought  to  an  un- 
timely end  by  high  living  and  drinking. 

The  rate  of  growth,  up  to  the  time  of  puberty  (the 
development  of  the  sexual  functions)  is  greater  in  girls 

145  ' 


146  PHYSIOLOGY   FOR   NURSES 

than  in  boys.  Girls  between  twelve  and  fifteen  are  bet- 
ter developed  than  boys  of  that  age,  while  beyond  fif- 
teen the  boy's  growth  is  stimulated  while  the  girl's  is 
moderated.  Consequently  the  male  overtakes  and  passes 
the  female.  Growth,  particularly  of  the  skeleton,  is 
not  arrested  by  underfeeding.  The  thymus  and  pitui- 
tary glands  form  hormones  which  stimulate  the  growth 
of  the  skeleton,  which  will,  in  the  underfed,  continue  to 
grow  at  the  expense  of  the  other  tissues,  notably  the 
muscles.  Possibly  some  such  internal  secretion,  or  the 
derangement  of  an  internal  secretion,  is  influential  in 
the  growth  of  tumors,  such  as  cancer.  Whether  man 
may  learn  to  control,  by  proper  diet,  the  rate  and 
amount  of  growth,  is  still  unknown;  but  the  indications 
are  that  a  further  knowledge  of  the  internal  secretions 
may  point  out  the  method  by  which  dwarfism  and 
gigantism  may  be  avoided  and  a  uniform  growth  may  be 
attained.  A  much  larger  proportion  of  ingested  food 
is  utilized  for  growth  in  the  lower  animals  than  in  man. 
In  a  large  number  of  mammals  it  has  been  determined 
that  340  out  of  every  thousand  calories  is  used  for 
growth,  while  man  employs  but  five  per  cent  for  the 
same  purpose. 

After  growth  ceases,  our  food  is  employed  in  creating 
energy  and  effecting  repair.  Gradually  the  protoplasm 
loses  its  power  of  growth,  maturity  is  reached,  decline 
begins,  and  death  finally  terminates  the  existence  of  the 
individual.  With  no  intervening  disease  or  injury,  and 
with  perfect  food  and  surroundings,  probably  the  ulti- 
mate end  would  be  reached  by  the  simultaneous  death, 
or  wearing  out,  of  all  the  tissues,  and  life  would  end 
like  the  wonderful  "One-Hoss  Shay"- 

"All  at  once  and  nothing  first, — 

Just  as  bubbles  do  when  they  burst, ' ' 


APPENDIX 

CHEMICOPHYSICS 

If  we  reflect  upon  all  that  surrounds  us,  even  our- 
selves, we  find  that  we  may  classify  the  sources  of  all 
our  impressions  under  the  heads  of  matter,  energy,  and 
spirit.  (Mallet) . 

Matter  is  any  thing  which  occupies  space.  Hence 
liquids,  gases  and  solids  are  all  forms  of  matter,  and  our 
common  experience  proves  that  these  substances  may  be 
measured  and  determined  to  have  length,  breadth,  and 
thickness  or  any  of  these  qualities.  When  matter  ex- 
tends in  but  one  direction  it  has  length;  when  in  two, 
we  speak  of  it  as  area. 

Mass  is  the  amount  of  matter  contained  in  any  body 
under  examination. 

Divisibility. — All  matter  is  capable  of  being  divided. 
We  may  break  up  a  piece  of  iron  or  one  of  chalk  into 
many  particles ;  but  finally  a  subdivision  is  reached  be- 
yond which  we  are,  so  far,  unable  to  go.  This  last  sub- 
division is  so  minute  as  to  be  invisible  and  is  called  an 
atom,  the  unit  by  which  different  forms  of  matter  unite 
with  similar  units  of  other  forms  to  create  combinations. 

Matter,  as  has  been  seen,  exists  in  three  states,  liquid, 
gaseous  and  solid.  Matter  in  any  state  has  its  peculiari- 
ties which  we  designate  the  properties  of  matter.  Thus 
a  body  may  be  elastic,  returning  to  its  original  form 
after  bending  or  twisting;  porous,  having  spaces  between 
its  particles  in  which  other  matter  may  insinuate  itself 
— an  apparent  exception  to  the  law  of  impenetrability, 

147 


148  PHYSIOLOGY   FOR   NURSES 

i.e.,  110  two  bodies  can  occupy  the  same  space  at  the 
same  time;  compressible,  depending  on  its  porosity;  and 
containing  properties  by  which  matter  may  be  converted 
into  energy. 

Energy  is  capacity  for  work  and  is  made  known  to 
us  by  changes  in  matter.  Some  of  the  many  forms  of 
energy  are  mechanical  energy,  gravity,  cohesion,  ad- 
hesion, heat,  light,  electricity,  and  chemical  energy. 

Mechanical  energy  changes  the  condition  of  masses 
of  matter  as  respects  motion  or  rest  (Mallet).  The  use 
of  water  to  turn  a  mill  wheel  is  an  illustration  of  me- 
chanical energy  by  that  natural  force  which  we  call  grav- 
ity. It  is  simply  the  weight  of  the  water  which  turns 
the  wheel.  If  the  water  is  too  small  in  quantity  or  the 
wheel  too  heavy,  no  movement  Avill  result.  If  the  mass 
of  water  is  great  in  proportion  to  the  resistance  of  the 
wheel,  the  motion  will  be  rapid.  Hence  mechanical 
energy  is  dependent  on  the  mass  to  be  moved. 

Gravity  is  the  mutual  attraction  Avhich  masses  of 
matter  exert  upon  each  other.  It  increases  with  the 
masses  concerned  and  decreases  with  their  distance  from 
one  another.  The  earth,  the  largest  mass  of  matter  with 
which  we  are  familiar,  attracts  whatever  is  unsupported 
in  proportion  to  its  density  and  the  measure  of  this 
attraction  is  the  weight  of  the  body.  Various  systems 
of  measuring  weight  are  used,  the  avoirdupois  in  Eng- 
lish-speaking countries  and  the  Metric  in  France.  The 
Metric  system,  however,  is  becoming  universal  in 
science. 

Specific  gravity,  or  specific  weight  means  the  weight 
of  a  given  body  when  compared  with  the  weight  of  a 
known  standard.  For  liquids  and  solids  the  standard 
is  distilled  water  at  four  degrees  centigrade,  and  for 
gases  hydrogen  at  zero  centigrade. 


APPENDIX  149 

Instruments  for  determining  the  specific  gravity  of 
liquids  are  called  hydrometers.  They  are  made  of  glass 
with  weight  in  the  bottom,  a  bulb  in  the  middle,  and  a 
stem  containing  a  scale  at  the  top.  When  placed  in  a 
liquid  they  sink  to  a  certain  level,  and  the  specific 
gravity  is  then  read  from  the  scale.  Specific  names  are 
given  modifications  of  these  instruments  intended  for 
definite  liquids,  as  urinometer,  lactometer,  etc.,  for  urine 
and  milk. 

Cohesion  and  Adhesion. — Cohesion  is  the  force  by 
which  the  particles  of  matter  of  the  same  kind  are  held 
together.  The  particles  of  a  bar  of  iron  for  instance 
cohere  or  are  held  together  by  cohesion.  Adhesion  is 
that  form  of  energy  by  which  masses  of  matter  of  dif- 
ferent kinds  are  held  together,  as  when  a  carpenter 
joins  two  pieces  of  wood  with  glue.  It  is  obvious  that 
cohesive  energy  must  be  exerted  in  greatly  different 
measure  in  different  masses.  It  is  powerfully  shown 
in  the  bar  of  iron  and  inappreciably  in  a  volume  of 
water.  Cohesion,  therefore,  acts  not  only  at  immeasur- 
ably small  distances,  but  with  such  varying  force  as  to 
determine  the  hardness  of  the  diamond  or  the  softness 
of  wax.  Adhesion  is  sometimes  employed  to  remove 
one  substance  from  another,  as  in  the  process  of  filtra- 
tion through  charcoal  to  remove  coloring  matter.  Matter 
is  said  to  be  hard  when  it  requires  great  force  to  scratch 
it ;  brittle,  when  it  breaks  only  from  violent  blows ;  tena- 
cious, when  it  resists  stretching;  malleable  when  it  can  be 
beaten  into  thin  sheets,  and  ductile  when  it  can  be  pulled 
out  into  fine  strands,  like  wire. 

Crystals  are  solid  substances  bounded  by  plane  faces 
and  definite  angles  (Bliss  and  Olive).  The  process  of 
forming  crystals  is  called  crystallization. 


150  PHYSIOLOGY   FOR   NURSES 

PROPERTIES  OF  LIQUIDS 

If  a  small  tube  is  inserted  into  a  glass  of  water  it 
will  be  seen  that  the  water  in  the  tube  rises  to  a  higher 
level  than  that  in  the  glass.  This  is  due  to  cohesion 
between  the  particles  of  water  and  adhesion  between 
the  water  and  the  tube,  the  adhesion  being,  in  this  case, 
the  stronger.  If  the  experiment  is  repeated,  but  mer- 
cury substituted  for  water,  the  column  in  the  tube  will 
be  lower  than  the  level  of  the  mercury  in  the  glass. 
Here  the  cohesion  of  the  particles  of  mercury  is  stronger 
than  the  adhesion  of  the  mercury  to  the  tube. 

Diffusion  is  another  property  of  liquids  by  which  two 
liquids  of  different  specific  gravity  will  mix  without  shak- 
ing even  though  the  lighter  be  placed  at  the  top.  This 
does  not  apply  to  liquids  not  soluble  in  each  other.  If  the 
two  liquids  are  separated  by  a  thin  membrane  they  will 
still  mix,  a  process  called  dialysis.  Some  fluids  will  not 
mix  in  this  way.  Those  which  diffuse  through  a  mem- 
brane are  called  crystalloid,  and  those  which  will  not  dif- 
fuse are  called  colloid. 

Solution. — When  matter,  solid,  liquid  or  gaseous,  is 
permanently  mixed  with  liquid,  forming  a  uniform  body 
which  does  not  separate  on  standing,  the  one  is  said  to 
be  dissolved  in  the  other,  or  a  solution  has  been  formed. 
The  most  familiar  example  is  the  solution  of  sugar  in 
coffee,  or  other  drink,  to  sweeten  it.  "When  it  is  de- 
sired to  separate  a  solid  from  a  liquid  in  which  it  has 
been  dissolved,  the  liquid  is  passed  through  some  porous 
material  to  which  the  solid  adheres,  leaving  the  liquid 
behind.  This  process  is  called  filtration.  Many  solids 
in  solution  can  not  be  extracted  by  this  process,  but 
some  can  be  with  much  saving  of  time  and  labor. 


APPENDIX  151 

PROPERTIES  OF  GASES 

The  most  striking  characteristic  of  all  gases  is  their 
tendency  to  expand  indefinitely  in.  all  directions,  espe- 
cially when  heated,  and  to  mix  with  other  gases  by  a 
process  similar  to  the  diffusion  of  liquids.  The  opposite 
character,  extreme  compressibility,  is  equally  striking. 
Indeed,  under  sufficient  pressure  accompanied  by  a  very 
lo\y  temperature,  gases  may  be  compressed  until  they 
become  liquid.  This  tendency  to  expansion  permits 
ventilation  by  the  simple  process  of  opening  the  window. 
The  warmer  gas  tends  to  expand  and  rise  to  the  window 
while  the  colder  gas  (air)  from  the  outside  tends  to 
sink  to  the  floor.  There  are  thus  two  currents  of  gas 
at  all  times,  one  entering  and  one  leaving  through  the 
same  opening.  The  atmospheric  air  is  composed  of 
gases  which,  however  light,  still  have  weight  sufficient 
to  exert  a  pressure  of  about  fifteen  pounds  to  the  square 
inch,  or  to  sustain  a  column  of  mercury  of  about  thirty 
inches  in  height.  It  is  upon  this  atmospheric  pressure 
that  the  barometer  is  based. 

HEAT,  LIGHT,  AND  ELECTRICITY 

Heat  is  a  form  of  m.otion.  Not  only  is  this  true,  but 
heat  may  be  converted  into  motion  or  motion  into  heat. 
All  matter,  even  the  densest,  is  supposed  to  contain 
minute  spaces  between  the  molecules  of  which  it  is  com- 
posed, which  spaces  are  filled  with  an  elastic  and  im- 
ponderable ether  which  permits  absolute  freedom  of 
vibratory  movement  of  the  particles.  If  the  movement 
is  at  a  rapid  rate,  the  heat  will  be  great;  if  at  a  lower 
velocity,  the  heat  will  be  less,  but  heat  is  always  present, 
even  in  ice.  This  is  called  the  undulatory  theory  of  heat. 

The  most  striking  constant  action  of  heat  is  to  cause 


152  PHYSIOLOGY  FOR   NURSES 

expansion.  If  the  expansion  is  in  but  one  direction,  it 
is  called  linear,  if  in  two,  superficial,  and  in  three  cubi- 
cal. Of  course  expansion  really  always  takes  place  in 
three  directions.  Thus  steel  rails  on  a  railway  expand 
chiefly  in  a  linear  direction,  because  their  bulk  in  this 
direction  is  greatest,  but  they  also  expand  superficially 
and  cubically.  Changes  in  volume,  therefore,  result 
from  increase  or  loss  of  heat.  Advantage  is  taken  of 
this  fact  to  make  the  instrument  with  which  the  degree 
of  heat  is  measured — the  thermometer.  Matter  which 
absorbs  moisture  contracts  under  the  influence  of  heat, 
because  the  rise  in  temperature  expels  the  moisture. 
Wood  and  paper  are  good  examples  of  such  bodies. 

Temperature  is  not  heat,  but  is  simply  a  measure  of 
the  ~hotness  of  a  given  body.  A  degree  of  temperature  is 
a  unit  for  measuring  hotness  as  a  stick  of  thirty-six 
inches  is  a  unit  for  measuring  goods.  The  thermometer 
is  simply  a  glass  tube  containing  a  substance  which  ex- 
pands rapidly  in  the  presence  of  heat  or  contracts  when 
some  of  the  heat  is  removed.  Mercury  and  alcohol  are 
the  two  substances  in  chief  use  for  this  purpose — mer- 
cury because  it  remains  liquid  in  any  but  extreme  heat 
or  cold,  and  alcohol  because  it  is  practically  unfreez- 
able. 

The  scale  of  a  thermometer  is  arrived  at  by  finding 
two  constant  points — that  of  melting  ice  and  that  of 
boiling  water.  In  the  centigrade  scale  the  melting  point 
of  ice  is  marked  zero,  while  in  the  Fahrenheit,  thirty- 
two  degrees  indicate  this  point.  The  boiling  point  of 
water  is  marked  100  in  centigrade  and  212  in  Fahren- 
heit. One  degree  Fahrenheit  is  equal  to  %  degree  centi- 
grade. To  convert  Fahrenheit  to  centigrade,  therefore, 
subtract  32  and  multiply  by  %. 

Example:     104°  -32  —  72.     72  x  %  —  360  =  40°  C. 

9 


APPENDIX  153 

To  convert  centigrade  into  Fahrenheit  multiply  by  9, 
divide  by  5,  and  add  32. 

Example:     36°  x  9  =  324.     324 -s- 5  =  64.8.     64.8  +  32  =  96.8°   F. 

Heat  is  transmitted  by  conduction,  radiation,  and 
convection.  Hold  a  poker  in  the  fire  until  the  end  is 
red  hot  and  you  will  find  the  part  in  the  hand  uncom- 
fortably warm.  This  is  heat  transmitted  by  conduction, 
Place  water  in  a  vessel  and  apply  heat  to  the  bottom. 
The  heated  particles  of  water  rise  to  the  top.  This  is 
transmitting  by  convection.  When  sitting  before  an  open 
fire  one  often  places  a  screen  between  the  fire  and  one's 
person  to  prevent  the  radiation  of  the  heat  rays.  If  the 
air  were  heated  uniformly  by  the  fire  the  screen  would  be 
no  protection.  This  is  radiation  of  heat. 

Heat  is  employed  to  liquefy  solids  (fusion),  to  alter 
organic  bodies  as  in  roasting,  to  separate  volatile  from 
less  volatile  matter  (vaporization),  to  destroy  organic 
life  as  in  sterilization  and,  particularly  by  the  chemist, 
in  many  other  processes. 

LIGHT 

Light  is  the  agent  which,  by  its  action  on  the  retina, 
excites  in  us  the  sensation  of  vision.  All  bodies,  as  well 
as  the  celestial  spaces,  are  filled  by  an  extremely  subtle 
elastic  medium,  which  is  called  the  luminiferous  ether. 
(Ganot).  The  luminosity  of  a  body  is  due  to  rapid 
vibrations  of  its  molecules.  These  vibrations  are  com- 
municated to  the  ether  and  through  it  to  the  terminals 
of  the  optic  nerve  in  the  retina. 

Sources  of  Light. — The  chief  source  of  light  is  the 
sun ;  but  light  is  obtained  by  chemical  combination,  heat, 
electricity  and  phosphorescence.  Heat  produces  light 
only  when  bodies  have  their  temperature  raised  to  five 


154  PHYSIOLOGY  FOR  NURSES 

or  six  hundred  degrees.  Chemical  combinations  pro- 
duce light  also  by  heat,  since  luminous  flames  are  simply 
gases  which  contain  solids  heated  to  incandescence. 
Phosphorescence  is  exhibited  by  decaying  wood,  or  fish, 
by  glowworms,  etc. 

Some  bodies,  like  wood,  metals  and  many  others,  com- 
pletely stop  light  and  are  called  opaque.  Others,  like 
glass,  air,  and  clear  water  allow  light  to  pass  and  are 
called  transparent  or  diaphanous;  while  others  permit 
only  a  portion  of  the  light  to  pass,  thin  porcelain  for 
instance,  and  are  said  to  be  translucent.  No  body  trans- 
mits all  of  the  light  which  falls  upon  it,  but  even  the 
most  transparent  absorb  some  of  the  rays. 

Propagation  of  Light. — A  medium  is  any  space  or  sub- 
stance which  light  can  traverse  (Ganot)  and  is  called 
homogeneous  when  its  density  is  the  same  in  all  parts, 
like  air.  Through  all  homogeneous  media  light  is  trans- 
mitted in  a  straight  line.  Light  emanates  from  a  lumi- 
nous body  in  all  directions  (Ganot),  but  changes  its  di- 
rection when  it  strikes  a  medium  of  different  density.  If 
the  new  medium  is  impenetrable,  light  will  be  reflected; 
if  penetrable,  refracted. 

When  a  beam  of  sunlight  passes  through  a  small  open- 
ing it  forms  a  small  pencil-like  bundle  of  rays.  If  these 
strike  a  polished  surface  they  are  bent  or  turned  away 
from  the  surface  at  the  same  angle  at  which  they  struck  it. 
The  angle  at  which  the  entering  sunbeam  struck  the 
polished  surface  is  called  the  angle  of  incidence;  while 
that  at  which  it  turns  away  is  called  the  angle  of  re- 
flection. The  rule,  therefore,  is  that  "the  angle  of  re- 
flection is  equal  to  the  angle  of  incidence."  As  is  the 
case  of  passing  through  a  medium,  not  all  the  light  is 
reflected,  but  some  is  always  absorbed  by  the  reflecting 
surface  while  some  is  irregularly  reflected  as  diffused 


APPENDIX  155 

light.  It  is  diffused  light  which  makes  nonluminous 
bodies  visible.  "From  the  inside  of  our  rooms  we  well 
see  external  objects,  for  they  are  powerfully  illumi- 
nated; but  from  the  outside  we  only  see  confusedly  the 
objects  in  the  interior  for  they  receive  but  little  light.'' 
It  is  the  great  diffusion  on  the  outside  and  the  slight 
amount  inside  which  causes  the  difference.  When  the 
room  is  illuminated  at  night  the  opposite  is  true. 

Refraction. — When  light  passes  obliquely  from  a  less 
dense  through  a  denser  medium  it  is  bent  away  from  its 
original  path  or  refracted  (from  a  Latin  word  meaning 
broken).  Glass  is  denser  than  air.  A  lens  is  a  piece  of 
glass  which  may  be  flat  on  one  side  and  hollow  on  the 
other — planoconcave — flat  on  one  side  and  bulging  on 
the  other — planoconvex, — bulging  on  both  sides — bi- 
convex or  double  convex, — or  concave  on  both  sides — 
biconcave  or  double  concave.  A  ray  passing  through 
the  exact  center  of  any  lens  is  not  bent;  but  a  ray  which 
strikes  obliquely,  as  any  ray  not  in  the  exact  center 
must  strike  on  concave  or  convex  surfaces,  is  bent  toward 
a  common  center  in  convex  and  away  from  the  center  in 
concave  lenses,  or  the  rays  are  converged  by  convex  and 
diverged  by  concave  lenses.  As  animal  eyes  have  double 
convex  lenses  which  do  not  always  fit  the  eye  in  which 
they  are  found,  oculists  make  use  of  this  principle  of 
refraction  to  place  glasses  in  front  of  the  eye  to  con- 
verge or  diverge  the  rays  and  thus  correct  the  refrac- 
tive error  of  the  natural  eye. 

The  point  at  which  all  of  the  rays  must  meet  after 
passing  through  a  lens  is  called  its  "focal  point."  The 
more  convex  a  lens,  the  nearer  to  the  lens  is  the  focal 
point ;  i.e.,  the  more  abruptly  it  breaks  or  bends  the  rays. 
The  path  through  the  center  of  the  lens  is  its  principal 
axis  and  parallel  rays  emitted  from  the  lens  are  con- 


156  PHYSIOLOGY  FOR  NURSES 

verged  to  this  principal  axis  forming  the  focus.  Con- 
cave lenses  diverge  the  rays  emitted  and  have  no  actual 
focus. 

Prisms. — "A  prism  is  any  transparent  medium  com- 
prised between  two  plane  faces  inclined  to  each  other." 
A  ray  of  light  passing  through  a  prism  is  not  only 
refracted,  but  is  broken  up  into  the  different  colors  of 
which  light  is  composed.  The  undulatory  theory  teaches 
that  light  is  dependent  upon  vibrations  of  the  ether. 
The  different  colored  rays  vibrate  at  different  rates — 
red,  the  slowest,  at  458  millions  of  millions  a  second, 
and  violet,  the  swiftest,  at  a  rate  of  727  millions  of 
millions  a  second.  Between  these  extremes  the  other 
colors  are  interspersed,  with  varying  rates  for  each,  in 
the  order,  violet,  indigo,  blue,  green,  yelloAv,  orange 
and  red. 

ELECTRICITY  AND  MAGNETISM 

"Symmers'  theory  assumes  that  every  body  contains 
an  indefinite  amount  of  subtile  imponderable  matter 
which  is  called  electrical  fluid,"  formed  by  the  union 
of  two  fluids  distinguished  as  positive  and  negative; 
that  in  the  natural  state  the  two  neutralize  each  other, 
but  that  they  can  be  separated  by  friction  and  other 
means,  one  never  appearing  without  the  other,  though 
either  may  be  present  in  excess  of  the  other,  so  that  a 
body  may  be  either  positively  or  negatively  electrified. 
"Electricities  of  the  same  kind  repel  one  another,  and 
electricities  of  opposite  kinds  attract  each  other." 
Electricity  circulates  freely  over  some  bodies  and  does 
not  circulate  over  others.  The  first  are  called  conduc- 
tors and  the  second  nonconductors. 

Electricity  may  be  frictional  when  produced  by  rub- 
bing, but  some  bodies,  like  glass,  give  positive  while 


APPENDIX  157 

others  give  negative  electricity.  "The  human  body, 
when  rubbed  with  silk,  becomes  negatively  charged, 
with  wool,  positively  charged." 

Chemical  electricity  is  the  result  of  the  action  of  an 
acid  on  two  metals,  frequently  zinc  and  carbon.  That 
which  is  acted  on  most  readily,  zinc  in  this  instance,  is 
called  the  positive  plate,  indicated  by  the  plus  sign  -)-, 
while  the  one  which  resists  the  acid  more  is  the  negative 
plate,  indicated  by  the  minus  sign  — . 

Such  plates,  united  by  copper  wires,  which  are  good 
conductors,  form,  when  immersed  in  an  acid  solution, 
a  galvanic  cell.  "The  ends  of  the  wires  leading  from 
the  plates  are  called  electrodes,  the  positive  plate  (+) 
called  the  cathode  or  negative  pole,  while  that  connected 
with  the  negative  plate  ( — )  is  the  anode  or  positive  pole. 
A  battery  is  a  combination  of  a  number  of  cells"  (Bliss 
and  Olive). 

Some  of  the  terms  employed  in  electrical  science  are 
the  volt,  or  unit  of  electromotive  force;  the  ampere  or 
unit  of  quantity  which  passes  through  a  standard  con- 
ductor in  a  given  time ;  the  o~hm  or  unit  of  resistance  of- 
fered by  a  copper  wire  250  feet  long  and  a  twentieth 
of  an  inch  thick,  and  the  watt,  or  unit  of  work. 

When  an  electric  current  is  passed  through  a  Crookes 
tube  it  produces  a  ray  which  has  the  power  of  passing 
through  and  illuminating  bodies  impenetrable  to  ordi- 
nary light.  These  are  called  "x-rays/'  or  Roentgen  rays, 
and  have  proved  of  immense  service  to  the  medical  pro- 
fession in  locating  foreign  bodies,  fractures  and  many 
other  conditions  formerly  very  obscure. 

MAGNETISM 

The  horseshoe  magnet,  so  familiar  as  a  toy,  is  the  com 
monest  and  best  known  display  of  magnetic  force.    Any 


158  PHYSIOLOGY  FOR   NURSES 

piece  of  steel  may  be  magnetized  and  when  this  has  been 
done,  it  is  found  to  have  a  positive  and  a  negative  pole, 
just  as  electricity.  If  the  rod  of  steel  so  treated  is 
broken  there  are  two  magnets,  each  with  its  two  poles, 
and  this  may  be  repeated  again  and  again  with  the  same 
result.  The  natural  magnet  is  an  oxide  of  iron  which 
has  the  power  of  attracting  other  metals.  Just  as  is  the 
case  with  the  electric  current,  like  poles  repel  and  un- 
like poles  attract  each  other. 

The  chief  use  of  magnetism  is  in  the  mariner's  com- 
pass which  enables  the  sailor  night  or  day,  cloudy  or 
fair,  always  to  know  the  direction  in  which  the  ship 
sails,  and  renders  navigation  a  thing  of  certainty  in- 
stead of  pure  guess  work.  It  is  of  great  service,  also, 
in  removing  minute  pieces  of  iron  or  steel  from  the  eye 
or  from  wounds  inflicted  by  such  fragments. 

CHEMISTRY 

Matter  is  constantly  undergoing  changes  which  are 
either  physical  or  chemical.  If  sugar  is  dissolved  in 
water,  neither  sugar  nor  water  is  changed.  The  sugar 
may  be  extracted  and  the  same  amounts  of  water  and 
sugar  remain.  But  when  iron  rusts  on  exposure  to  air, 
a  part  of  the  iron  has  joined  some  of  the  oxygen  of  the 
air  and  a  new  product  has  been  formed.  The  first  case 
is  purely  physical  and  the  second  chemical.  The  first 
is  a  mixture,  the  second  a  chemical  combination.  In  the 
first  illustration  neither  substance  has  been  changed  in 
character;  in  the  second  both  have  been  altered,  and, 
while  in  either  the  process  may  be  reversed  and  both 
elements  recovered,  the  method  of  recovery  is  different 
—the  one  physical  and  the  other  chemical.  Chemical 
changes  are  called  reactions  and  are  of  two  kinds,  i.e., 


APPENDIX  159 

synthetic,  when  combinations  are  made,  and  analytic 
Avhen  they  are  broken  up.  The  force  which  makes  two 
or  more  elements -unite  to  form  a  new  mass  of  matter  is 
called  chemical  affinity  and  acts  on  different  elements 
with  varying  degrees  of  violence  at  inappreciable  dis- 
tances. 

"  Chemistry  is  that  science  which  treats  of  the  com- 
position of  matter  and  the  changes  in  composition." 
(Bliss  and  Olive). 

Elements. — Those  substances  which  have  resisted 
every  effort  to  reduce  .them  to  simpler  forms  are  known 
as  elements.  Iron,  silver,  gold,  potash,  soda,  oxygen, 
etc.,  are  examples  of  these  primary  bodies.  A  table  of 
elements  with  their  atomic  weights  and  symbols  is  ap- 
pended. To  save  space  and  time,  the  whole  name  of  an 
element  is  not  written  when  a  chemical  combination  is 
to  be  expressed  by  a  formula,  but  the  first  letter  of  the 
name  of  the  element  is  used  as  a  capital,  followed  by  a 
small  letter  taken  from  the  name  when  the  names  of 
two  elements  begin  with  the  same  letter.  Thus  H  is 
the  symbol  of  hydrogen  and  Hg  the  symbol  of  mercury, 
the  official  name  of  which  is  hydrargyrum;  or  Fe  (fer- 
rum)  iron,  while  F  stands  for  fluorine.  Elements  can 
not  be  divided  into  simpler  bodies,  but  every  element 
is  composed  of  invisible  particles  called  atoms  and  as 
atoms,  however  small,  none  the  less  have  weight,  the 
symbols  of  the  elements  represent  an  atom  of  that 
element  which  has  a  weight,  as  compared  with  some 
other  element  used  as  a  standard,  called  its  atomic 
weight.  As  hydrogen  is  the  lightest  of  known  elements, 
it  has  been  selected  as  the  standard.  The  symbol  "H" 
means  one  atom  of  hydrogen  having  a  weight  repre- 
sented by  the  figure  1,  while  the  volume  of  oxygen  of 
the  same  cubic  measure,  Q£  the,  volume  of  hydrogen  is 


160  PHYSIOLOGY   FOR   NURSES 

found  to  weigh  15.88  times  the  volume  of  hydrogen. 
Therefore,  in  the  table  of  elements,  hydrogen  is  repre- 
sented by  the  letter  "H"  and  its  atomic  weight  by  the 
figure  1,  Avhile  oxygen  is  represented  by  the  symbol  or 
letter  "0"  and  its  atomic  weight  by  the  figures  15.88. 
In  the  same  way  uranium,  the  heaviest  of  all  elements, 
is  represented  by  the  symbol  "U,"  and  the  atomic 
weight  by  the  figures  239.5 — i.e.,  it  is  two  hundred  thirty- 
nine  and  a  half  times  heavier  than  hydrogen  with 
which  it  is  compared.  Atoms,  of  course,  can  not  be 
separated  and  weighed ;  so  the  atomic  weight  is  not  an 
actual  but  a  relative  weight,  When  more  than  one 
atom  occurs  in  any  chemical  combination,  small  figures 
placed  at  the  right  of  the  symbol  indicate  the  number 
of  atoms  engaged  in  that  combination.  Thus  H20  means 
two  atoms  of  hydrogen  combined  with  one  of  oxygen 
to  form  the  chemical  combination  of  water.  These  three 
atoms,  thus  united,  form  a  molecule,  and  the  molecular 
weight  of  a  substance  is  the  sum  of  the  atomic  weights  of 
the  elements  entering  into  its  combination. 

Examples:     H..O  =  Hydrogen  2  atoms  weighing      2 

Oxygen       1  atom         "  15.88 

Molecular  weight  of  water  17.88 

The  formula  of  ammonia  is  H3N  or 

Hydrogen   3   atoms  weighing     3 
Nitrogen     1  atom         "  13.93 

Molecular  weight  of  ammonia  16.93 

Hydrochloric  acid  is  represented  by  the  formula  HC1  or 
Hydrogen  1  atom  weighing        1 
Chlorine     1      "  "  35.18 


Molecular  weight  of  hydrochloric  acid  36.18 

It   will   be    noted    that    in    these    three    combinations, 
'hydrogen  is  represented  by  one,  two,  and  three  atoms 


APPENDIX  161 

for  chlorine,  oxygen  and  ammonia.  The  number  of 
atoms  of  each  element  required  to  enter  into  combina- 
tion with  another  element  is  called  valence,  or  "that 
property  of  an  element  which  determines  the  number 
of  atoms  of  another  element  which  its  atom  can  hold 
in  combination."  One  atom  of  hydrogen  can  never  hold 
in  combination  more  than  one  atom  of  another  element. 
For  this  reason  hydrogen  is  the  standard  of  measure 
for  valence  as  well  as  for  atomic  weight.  Those  ele- 
ments which  combine  with  one  atom  of  hydrogen  are 
called  monads,  or  univalent,  with  two,  diads,  or  diva- 
lent, with  three,  triads  or  trivalent  etc. 

In  writing  out  the  result  of  chemical  changes  one 
finds  that  all  the  elements  entering  into  the  change  can 
be  expressed  by  an  equation  in  which  the  signs  -f-  or  — , 
and  of  equality  ==,  may  be  employed,  every  atom  in  the 
substances  on  the  left  of  the  sign  of  equality  must  be  ac- 
counted for  on  the  right  of  that  sign,  if  the  change  is 
correctly  interpreted.  Thus :  nitrate  of  silver,  when 
acted  on  by  hydrochloric  acid,  is  changed  into  chloride 
of  silver  and  nitric  acid  expressed  by  the  following 
equation : 

AgN03  +  HC1  ==  AgCl  +  HN03 

On  the  left  we  have  one  atom  of  silver,  one  of  nitrogen 
and  three  of  oxygen,  combined  to  form  nitrate  of  silver. 
To  this  we  add  one  atom  of  hydrogen  and  one  of 
chlorine,  combined  to  form  hydrochloric  acid.  The 
change  which  takes  place  is  that  the  chlorine  displaces 
the  molecule  N03  which  is  joined  by  the  hydrogen  and 
the  result  is  that  011  the  right  we  now  have  one  atom 
of  silver  combined  with  one  of  chlorine,  forming  chloride 
of  silver,  while  one  atom  of  hydrogen  has  joined  one  of 
nitrogen  and  three  of  oxygen  to  form  nitric  acid;  but, 


162  PHYSIOLOGY   FOR   NURSES 

while  we  have  two  new  substances,  we  have  exactly 
the  same  number  of  atoms.  Such  changes  result  when 
the  chemical  affinity  of  one  element  is  stronger  than  that 
of  another.  In  this  example  nitrogen,  an  inert  sub- 
stance whose  chemical  affinities  are  not  strong,  is  re- 
placed by  chlorine  whose  affinity  is  strong  and  active. 

Acids. — "An  acid  is  a  substance  consisting  of  hydro- 
gen and  a  nonmetallic  element  or  radical,  which  usually 
has  a  sour  taste,  turns  litmus  red,  and  is  capable  of 
reacting  with  a  base  to  form  a  salt  and  water."  In  the 
example  given  above  the  radical  (the  nonmetallic  ele- 
ment which  combined  with  hydrogen)  is  made  up  of 
one  atom  of  nitrogen  and  three  of  oxygen.  When, 
therefore,  acids  combine  with  bases  to  form  salts,  it  is 
the  radical  which  thus  combines,  i.e.,  in  silver  nitrate 
AgN03,  the  nitric  acid  having  lost  its  hydrogen  which 
combined  with  0  to  form  water  and  was  replaced  by 
an  atom  of  H. 

Acids  which  have  but  one  element  of  H  to  be  replaced 
in  combination  with  bases  are  called  monobasic,  those 
with  two,  dibasic,  etc. 

Bases. — "A  base  is  a  compound  in  which  a  metallic 
element  is  linked  to  hydrogen  by  means  of  oxygen, 
turns  litmus  blue,  and  is  capable  of  reacting  with  an 
acid,  forming  a  salt  and  water." 

Bases  have  a  group  of  oxygen  and  hydrogen  (OH) 
atoms  called  Jiydroxyl  and  the  bases  themselves  are  called 
hydroxides.  If  there  is  one  OH  group  the  base  is  mono- 
acid,  if  two,  diacid,  etc. 

Salts. — These  substances  are  "products  of  the  inter- 
action of  acids  and  bases."  A  base  like  sodium  hydrox- 
ide may  be  converted  into  common  table  salt  (sodium 
chloride)  and  water.  The  change  is  expressed  in  the 
following  formula : 


APPENDIX  163 

NaOH  4-  HOI  NaCl         -f     H2O 

Sodium  Hydroxide      Hydrochloric  acid      Sodium  Chloride      Water 

One  atom  of  soda  (Na)  looses  a  molecule  composed 
of  an  atom  of  0  and  one  of  H,  and  is  joined  by  an  atom 
of  chlorine  taken  from  a  molecule  of  hydrochloric  acid 
whose  hydrogen  made  the  second  atom  of  that  element 
necessary  to  form  a  molecule  of  water. 

It  was  never  the  writer's  intention  to  compose  a  text- 
book of  chemistry  and  physics  but  to  give  a  bare  out- 
line which  would  be  of  assistance  to  those  students  of 
physiology  who  have  not  had  a  proper  course  in  those 
subjects.  The  student  is,  therefore,  referred  to  regular 
works  for  further  enlightenment. 


164 


PHYSIOLOGY   FOR   NURSES 


SYMBOLS  AND  ATOMIC  MASSES  (' 
ELEMENTS 


WEIGHTS")  OF  THE 


NAME 


SYMBOL 


Aluminum, Al 

Antimony  (Stibium'),  ...  Sb 

Argon, A 

Arsenic, j  As 

Barium, !  Ba 

Beryllium; Be 

Bismuth, Bi 

Boron, .  B 

Bromine, Br 

Cadmium, Cd 

Cfesium, Cs 

Calcium, Ca, 

Carbon, C 

Cerium, Ce 

Chlorine, Cl 

Chromium, Cr 

Cobalt, Co 

Copper   (Cuprum),  ....  Cu 

Erbium,       ? Eb 

Fluorine, F 

Gadolinium,     ? Gd 

Gallium, Ga 

Germanium, Ge 

Gold    (Aurum), Au 

Helium, He 

Holmium,   ? Ho 

Hydrogen H 

Indium, In 

Iodine, I 

Iridium, Ir 

Iron   (Ferrum), Fe 

Krypton, Kr 

Lanthanum, La 

Lead   (Plumbum),  ....  Pb 

Lithium,  . Li 

Magnesium, Mg 

Manganese, Mn 

Mercury   (Hydrargyrum},     .  Hg 

Molybdenum, Mo 

Neodymium, Nd 


ATOMIC 
WEIGHT 


26.9 

119.1 
39.6 
74.4 

136.4 
9.03 

206.9 
10.9 
79.36 

111.6 

132. 
39.7 
11.91 

139. 
35.18 
51.7 
58.56 
63.1 

164.8 
18.9 

155. 
69.5 
71.5 

195.7 
4. 

162. 
1. 

113.1 

125.9 

191.5 
55.6 
81.2 

137. 

205.35 
6.98 
24.18 
54.6 

198.8 
95.3 

142.5 


AT.    WT. 

(approx.) 


27. 
119. 

74.5 
136.5 

9. 
207. 

11. 

79.5 


40. 
12. 


63. 

19. 


1. 

126. 
55.5 


205.5 
7. 

24. 

54.5 
199. 


165 


SYMBOLS  AND  ATOMIC  MASSES  ( 
ELEMENTS 


WEIGHTS")  OF  THE 


NAME 


SYMBOL 


Neon, Ne 

Nickel, Ni 

Niobium, Nb 

Nitrogen, N 

Osmium, '  Os 

Oxygen, '  O 

Palladium, '  Pd 

Phosphorus, P 

Platinum, Pt 

Polonium,       ? Po 

Potassium,   (Kalium)   ...  K 

Praseodymium, Pr 

Radium,      ? '  Ka 

Rhodium, Ro 

Rubidium,         Rb 

Ruthenium, '  Ru 

Samarium,      ? Sa 

Scandium,         Sc 

Selenium, Se 

Silicon,         Si 

Silver,    (Argentum)      .     .     .  Ag 

Sodium,    (Natrium)     .     .     .  Na 

Strontium, Sr 

Sulphur,  .   . S 

Tantalum, Ta 

Tellurium, Te 

Terbium     .      ? Tb 

Thallium, 

Thorium, Th 

Thulium,    .     I Tu 

Tin    (Stannum) Sn 

Titanium Ti 

Tungsten   (Wolfram)   ...  W 

Uranium, Ur 

Vanadium, V 

Xenon, X 

Ytterbium,  .         ?     .     .     .     .  Yb 

Yttrium,  . Yt 

Zinc, Zn 

Zirconium, Zr 


ATOMIC 
WEIGHT 


19.9 
58.3 

93.3 
13.93 

189.6 
15.88 

105.2 
30.77 

193.3 

? 
38.86 

139.4 
» 

102.2 
84.76 

100.9 

148.9 
43.8 
78.5 
28.2 

107.12 
22.88 
86.94 
31.83 

181.6 

126. 

158.8 

202.6 

230.8 

170. 

117.6 
47.7 

182.6 

237.7 
50.8 

127. 

172. 
88.3 
64.9 
90. 


AT.    WT. 

(approx.) 


14. 
16. 

31. 
193.5 

39. 


28. 
107. 
23. 
87. 
32. 


117.5 


65. 


INDEX 


Abdecens  nerve,   115 
Absorption,    intestines,    63 

stomach,  59 
Accommodation,  129 
Adrenal   glands,   94 
Afferent  nerves,  99-100  . 
Air,  amount,  38 

alterations   of,    41 

composition,  40 

diffusion   of,    39 
Arterial  circulation,  24 
Arteries,  27 
Asphyxia,    39 
Auditory   canal,   136 
Auricles,  24 


Bile  in  digestion,  78 
Bilirubin,  76 
Bdliverdin,   76 
Bladder,  87 
Blood,    19 

coagulation,  22 

composition,  19 

plasma,  19 

pressure,   30 

serum,  19 
Brain,  102 


Capillaries,  31 
Capsule,   internal,   107 
Carbohydrates,    45-64 
Carbon,   1-41 
Cardiac  cycle,  25 
Cerebellum,  107 
Cerebrum,   102 

motor  centers,  103 

sensory,    103 


Chorda  tympani,  116 
Choroid  coat,  130 
Chyme,  60 
Ciliary  muscle,  130 
Circulation,  25-29 

pulmonary,  24 

systemic,  24 
Colloids,    150 
Common  bile  duct,  77 
Complemental  air,  38 
Convoluted  tubules,  87 
Cornea,   130 

Corpora  quadrigeir.ina,  107 
Coughing,  39 
Cranial  nerves,  114 
Crossed  pyramidal  tracts,  113 
Crura  cerebri,   106 
Cutaneous    sensations,   92f 


Death,  145 
Defecation,  54 
Deglutition,  51 
Diffusion,  39 

in  lungs,  34 
Digestion,  141 
Dreams,  141 
Dyspnea,  38 

E 

Ear,  134 

Eighth  nerve,  135 
Eleventh  nerve,  115 
Enzymes,   48 
Expiration,  37 
Eyeball,  130 


Facial  nerve,  116 
Fats,  45 

absorption  of,  64 


166 


INDEX 


167 


Feces,  65 
Fibrin,   22 
Fifth  nerve,  115 
First  nerve,  114 
Food  digestion,  43 
Food  tables,  47 
Fourth  nerve,   114 

G 

Gastric   digestion,    57 
Gastric  juice,  57 
Glands,   ductless,  94 

mammary.    1-14 

salivary,  55 

sweat,  90 

thyroid,  95 
Glomeruli,   85 

Glossopharyngeal   nerve,    116 
Glycogen,   79 
Gustatory  center,  123 

H 

Hearing,   133 
Heart,   23 

diastole,  25 

systole,  25 

valves,  24 
Heat,  151 
Hemoglobin,    20 
Henle,  loops   of,    (see   Kidney) 
Hiccough,    39 
Hunger   pains,    55 
Hydrochloric  acid;   51 
Hydrogen,   160 
Hypermetropic,  132 
Hypoglossal  nerve,  115 


Ileocecal  valve,  53 
Inspiration,   35 
Intestine,  movements  in,  53 
Iris,  130 


Kidney,  82 

secretion  of,  82 
structure,  85 


Large  intestine,  53 

Laughing,    39 

Lens,  130 

Leucocytes,  21 

Liver,  76 

Lungs,    (see  Respiration) 

Lymph,  21 

M 

Mammary   glands,    144 
Mastication,  51 
Medulla   oblongata,   107 
Menstruation,   142 
Micturition,   88 
Milk,  47 
Mitral  valve,  24 
Motor  region  brain,  103 
Myopia,  131 

N 

Nervous  system,  99 
Nitrogenous  food,  44 


Olfactory  sense,  124 
Optic  nerve,   124 
Ovary,  142 


Pancreas,  97 
Pancreatic  juice,   61 
Perspiration,   90 
Pituitary  body,  97 
Placenta,  143 
Pneumogastric  nerve,  116 
Pons  varolii,  106 
Presbyopia,  133 
Protein,   44 
Ptyalin,  57 
Pulse,  29 
Pupil,  130 

R 

Rectum,  54 
Red  corpuscles,  20 
Reflex  action,  58-99 
Refraction,  128 
Renal  tubules,  85 


168 


INDEX 


Rennin,  59 
Residual  air,  38 
Respiration,   34 


S 


Salivary   glands,    55 
Salts,  44,  162    ' 
Sebaceous    glands,   91 
Semilunar  valves,  25 
Sensation,  skin,  92 
Senses,    special,    122 
Seventh  nerve,  116 
Sighing,  39 
Sight,  125 
Skin,  90 
Sleep,   138 
Smell,  124 
Spinal  cord,  112 
Stomach,  51 
Succus  entericus,  62 
Sweat  glands,  90 

composition  of,  90 
Sympathetic    system,    119 
Systole,   25 


Tactile   sensibility,   92 
Taste,  122 
Temperature,  152 
Tenth  nerve,  116 
Thirst,  55 
Thoracic  duct,  64 
Thyroid    gland,    95 
Touch,    92 
Tricuspid   valve,   24 
Trypsin,   61 
Tympanum,  134 

U 

Urea,  found  in  liver,   79 

excretion    of,    83 
Uric   acid,    83 
Urine,    82 


Vasomotor  nerves,  121 
Ventricles    of    heart,    24 
Vision,   125 
Vomiting,    54 

W 

White  corpuscles,  20 


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